possible deadlock in io_submit_one (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 17da61ae Add linux-next specific files for 20190814
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=127712e2600000
kernel config: https://syzkaller.appspot.com/x/.config?x=4733704ca85aaa66
dashboard link: https://syzkaller.appspot.com/bug?extid=af05535bb79520f95431
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+af0553...@syzkaller.appspotmail.com

=====================================================
WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
5.3.0-rc4-next-20190814 #66 Not tainted
-----------------------------------------------------
syz-executor.1/25024 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
ffff8880a374bbe8 (&fiq->waitq){+.+.}, at: spin_lock
include/linux/spinlock.h:338 [inline]
ffff8880a374bbe8 (&fiq->waitq){+.+.}, at: aio_poll fs/aio.c:1748 [inline]
ffff8880a374bbe8 (&fiq->waitq){+.+.}, at: __io_submit_one fs/aio.c:1822
[inline]
ffff8880a374bbe8 (&fiq->waitq){+.+.}, at: io_submit_one+0xefa/0x2ef0
fs/aio.c:1859

and this task is already holding:
ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq
include/linux/spinlock.h:363 [inline]
ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll
fs/aio.c:1746 [inline]
ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one
fs/aio.c:1822 [inline]
ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at:
io_submit_one+0xeb5/0x2ef0 fs/aio.c:1859
which would create a new lock dependency:
(&(&ctx->ctx_lock)->rlock){..-.} -> (&fiq->waitq){+.+.}

but this new dependency connects a SOFTIRQ-irq-safe lock:
(&(&ctx->ctx_lock)->rlock){..-.}

... which became SOFTIRQ-irq-safe at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
_raw_spin_lock_irq+0x60/0x80 kernel/locking/spinlock.c:167
spin_lock_irq include/linux/spinlock.h:363 [inline]
free_ioctx_users+0x2d/0x490 fs/aio.c:618
percpu_ref_put_many include/linux/percpu-refcount.h:293 [inline]
percpu_ref_put include/linux/percpu-refcount.h:309 [inline]
percpu_ref_call_confirm_rcu lib/percpu-refcount.c:130 [inline]
percpu_ref_switch_to_atomic_rcu+0x4c0/0x570 lib/percpu-refcount.c:165
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch kernel/rcu/tree.c:2157 [inline]
rcu_core+0x581/0x1560 kernel/rcu/tree.c:2377
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2386
__do_softirq+0x262/0x98c kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x19b/0x1e0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:536 [inline]
smp_apic_timer_interrupt+0x1a3/0x610 arch/x86/kernel/apic/apic.c:1095
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
constant_test_bit arch/x86/include/asm/bitops.h:207 [inline]
test_bit include/asm-generic/bitops-instrumented.h:238 [inline]
test_ti_thread_flag include/linux/thread_info.h:84 [inline]
need_resched include/linux/sched.h:1827 [inline]
mutex_spin_on_owner+0x7b/0x330 kernel/locking/mutex.c:568
mutex_optimistic_spin kernel/locking/mutex.c:673 [inline]
__mutex_lock_common kernel/locking/mutex.c:959 [inline]
__mutex_lock+0x330/0x13c0 kernel/locking/mutex.c:1103
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
addrconf_dad_work+0xad/0x1150 net/ipv6/addrconf.c:4032
process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

to a SOFTIRQ-irq-unsafe lock:
(&fiq->waitq){+.+.}

... which became SOFTIRQ-irq-unsafe at:
...
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x1f3/0x3c0 fs/fuse/dev.c:415
fuse_request_queue_background+0x2f8/0x5a0 fs/fuse/dev.c:676
fuse_request_send_background+0x58/0x110 fs/fuse/dev.c:687
cuse_send_init fs/fuse/cuse.c:459 [inline]
cuse_channel_open+0x5ba/0x830 fs/fuse/cuse.c:519
misc_open+0x395/0x4c0 drivers/char/misc.c:141
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4df/0x1250 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3416 [inline]
path_openat+0x10e9/0x4630 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_openat fs/open.c:1124 [inline]
__se_sys_openat fs/open.c:1118 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1118
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Possible interrupt unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&fiq->waitq);
local_irq_disable();
lock(&(&ctx->ctx_lock)->rlock);
lock(&fiq->waitq);
<Interrupt>
lock(&(&ctx->ctx_lock)->rlock);

*** DEADLOCK ***

1 lock held by syz-executor.1/25024:
#0: ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq
include/linux/spinlock.h:363 [inline]
#0: ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll
fs/aio.c:1746 [inline]
#0: ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one
fs/aio.c:1822 [inline]
#0: ffff88806001fc58 (&(&ctx->ctx_lock)->rlock){..-.}, at:
io_submit_one+0xeb5/0x2ef0 fs/aio.c:1859

the dependencies between SOFTIRQ-irq-safe lock and the holding lock:
-> (&(&ctx->ctx_lock)->rlock){..-.} {
IN-SOFTIRQ-W at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock_irq
include/linux/spinlock_api_smp.h:128 [inline]
_raw_spin_lock_irq+0x60/0x80
kernel/locking/spinlock.c:167
spin_lock_irq include/linux/spinlock.h:363 [inline]
free_ioctx_users+0x2d/0x490 fs/aio.c:618
percpu_ref_put_many include/linux/percpu-refcount.h:293
[inline]
percpu_ref_put include/linux/percpu-refcount.h:309
[inline]
percpu_ref_call_confirm_rcu lib/percpu-refcount.c:130
[inline]
percpu_ref_switch_to_atomic_rcu+0x4c0/0x570
lib/percpu-refcount.c:165
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch kernel/rcu/tree.c:2157 [inline]
rcu_core+0x581/0x1560 kernel/rcu/tree.c:2377
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2386
__do_softirq+0x262/0x98c kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x19b/0x1e0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:536 [inline]
smp_apic_timer_interrupt+0x1a3/0x610
arch/x86/kernel/apic/apic.c:1095
apic_timer_interrupt+0xf/0x20
arch/x86/entry/entry_64.S:830
constant_test_bit arch/x86/include/asm/bitops.h:207
[inline]
test_bit include/asm-generic/bitops-instrumented.h:238
[inline]
test_ti_thread_flag include/linux/thread_info.h:84
[inline]
need_resched include/linux/sched.h:1827 [inline]
mutex_spin_on_owner+0x7b/0x330
kernel/locking/mutex.c:568
mutex_optimistic_spin kernel/locking/mutex.c:673
[inline]
__mutex_lock_common kernel/locking/mutex.c:959 [inline]
__mutex_lock+0x330/0x13c0 kernel/locking/mutex.c:1103
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
addrconf_dad_work+0xad/0x1150 net/ipv6/addrconf.c:4032
process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
INITIAL USE at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:128
[inline]
_raw_spin_lock_irq+0x60/0x80
kernel/locking/spinlock.c:167
spin_lock_irq include/linux/spinlock.h:363 [inline]
free_ioctx_users+0x2d/0x490 fs/aio.c:618
percpu_ref_put_many include/linux/percpu-refcount.h:293
[inline]
percpu_ref_put include/linux/percpu-refcount.h:309
[inline]
percpu_ref_call_confirm_rcu lib/percpu-refcount.c:130
[inline]
percpu_ref_switch_to_atomic_rcu+0x4c0/0x570
lib/percpu-refcount.c:165
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch kernel/rcu/tree.c:2157 [inline]
rcu_core+0x581/0x1560 kernel/rcu/tree.c:2377
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2386
__do_softirq+0x262/0x98c kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x19b/0x1e0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:536 [inline]
smp_apic_timer_interrupt+0x1a3/0x610
arch/x86/kernel/apic/apic.c:1095
apic_timer_interrupt+0xf/0x20
arch/x86/entry/entry_64.S:830
constant_test_bit arch/x86/include/asm/bitops.h:207
[inline]
test_bit include/asm-generic/bitops-instrumented.h:238
[inline]
test_ti_thread_flag include/linux/thread_info.h:84
[inline]
need_resched include/linux/sched.h:1827 [inline]
mutex_spin_on_owner+0x7b/0x330 kernel/locking/mutex.c:568
mutex_optimistic_spin kernel/locking/mutex.c:673 [inline]
__mutex_lock_common kernel/locking/mutex.c:959 [inline]
__mutex_lock+0x330/0x13c0 kernel/locking/mutex.c:1103
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
addrconf_dad_work+0xad/0x1150 net/ipv6/addrconf.c:4032
process_one_work+0x9af/0x1740 kernel/workqueue.c:2269
worker_thread+0x98/0xe40 kernel/workqueue.c:2415
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
}
... key at: [<ffffffff8ab00360>] __key.54228+0x0/0x40
... acquired at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
aio_poll fs/aio.c:1748 [inline]
__io_submit_one fs/aio.c:1822 [inline]
io_submit_one+0xefa/0x2ef0 fs/aio.c:1859
__do_sys_io_submit fs/aio.c:1918 [inline]
__se_sys_io_submit fs/aio.c:1888 [inline]
__x64_sys_io_submit+0x1bd/0x570 fs/aio.c:1888
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe


the dependencies between the lock to be acquired
and SOFTIRQ-irq-unsafe lock:
-> (&fiq->waitq){+.+.} {
HARDIRQ-ON-W at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142
[inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x1f3/0x3c0 fs/fuse/dev.c:415
fuse_request_queue_background+0x2f8/0x5a0
fs/fuse/dev.c:676
fuse_request_send_background+0x58/0x110
fs/fuse/dev.c:687
cuse_send_init fs/fuse/cuse.c:459 [inline]
cuse_channel_open+0x5ba/0x830 fs/fuse/cuse.c:519
misc_open+0x395/0x4c0 drivers/char/misc.c:141
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4df/0x1250 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3416 [inline]
path_openat+0x10e9/0x4630 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_openat fs/open.c:1124 [inline]
__se_sys_openat fs/open.c:1118 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1118
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
SOFTIRQ-ON-W at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142
[inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x1f3/0x3c0 fs/fuse/dev.c:415
fuse_request_queue_background+0x2f8/0x5a0
fs/fuse/dev.c:676
fuse_request_send_background+0x58/0x110
fs/fuse/dev.c:687
cuse_send_init fs/fuse/cuse.c:459 [inline]
cuse_channel_open+0x5ba/0x830 fs/fuse/cuse.c:519
misc_open+0x395/0x4c0 drivers/char/misc.c:141
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4df/0x1250 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3416 [inline]
path_openat+0x10e9/0x4630 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_openat fs/open.c:1124 [inline]
__se_sys_openat fs/open.c:1118 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1118
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
INITIAL USE at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142
[inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x1f3/0x3c0 fs/fuse/dev.c:415
fuse_request_queue_background+0x2f8/0x5a0
fs/fuse/dev.c:676
fuse_request_send_background+0x58/0x110 fs/fuse/dev.c:687
cuse_send_init fs/fuse/cuse.c:459 [inline]
cuse_channel_open+0x5ba/0x830 fs/fuse/cuse.c:519
misc_open+0x395/0x4c0 drivers/char/misc.c:141
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4df/0x1250 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3416 [inline]
path_openat+0x10e9/0x4630 fs/namei.c:3533
do_filp_open+0x1a1/0x280 fs/namei.c:3563
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_sys_openat fs/open.c:1124 [inline]
__se_sys_openat fs/open.c:1118 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1118
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
}
... key at: [<ffffffff8ab9a180>] __key.45697+0x0/0x40
... acquired at:
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
aio_poll fs/aio.c:1748 [inline]
__io_submit_one fs/aio.c:1822 [inline]
io_submit_one+0xefa/0x2ef0 fs/aio.c:1859
__do_sys_io_submit fs/aio.c:1918 [inline]
__se_sys_io_submit fs/aio.c:1888 [inline]
__x64_sys_io_submit+0x1bd/0x570 fs/aio.c:1888
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe


stack backtrace:
CPU: 0 PID: 25024 Comm: syz-executor.1 Not tainted 5.3.0-rc4-next-20190814
#66
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x172/0x1f0 lib/dump_stack.c:113
print_bad_irq_dependency kernel/locking/lockdep.c:2095 [inline]
check_irq_usage.cold+0x586/0x6fe kernel/locking/lockdep.c:2293
check_prev_add kernel/locking/lockdep.c:2480 [inline]
check_prevs_add kernel/locking/lockdep.c:2581 [inline]
validate_chain kernel/locking/lockdep.c:2971 [inline]
__lock_acquire+0x25d0/0x4e70 kernel/locking/lockdep.c:3955
lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4487
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
aio_poll fs/aio.c:1748 [inline]
__io_submit_one fs/aio.c:1822 [inline]
io_submit_one+0xefa/0x2ef0 fs/aio.c:1859
__do_sys_io_submit fs/aio.c:1918 [inline]
__se_sys_io_submit fs/aio.c:1888 [inline]
__x64_sys_io_submit+0x1bd/0x570 fs/aio.c:1888
do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459829
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f9e07853c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459829
RDX: 0000000020000440 RSI: 0000000000000001 RDI: 00007f9e07833000
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9e078546d4
R13: 00000000004c0c19 R14: 00000000004d3c40 R15: 00000000ffffffff


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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[Eric Biggers]

From: Eric Biggers <ebig...@google.com>

When IOCB_CMD_POLL is used on the FUSE device, aio_poll() disables IRQs
and takes kioctx::ctx_lock, then fuse_iqueue::waitq.lock.

This may have to wait for fuse_iqueue::waitq.lock to be released by one
of many places that take it with IRQs enabled. Since the IRQ handler
may take kioctx::ctx_lock, lockdep reports that a deadlock is possible.

Fix it by always disabling IRQs when taking fuse_iqueue::waitq.lock.

Reproducer:

#include <fcntl.h>
#include <stdio.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <linux/aio_abi.h>

int main()
{
char opts[128];
int fd = open("/dev/fuse", O_RDWR);
aio_context_t ctx = 0;
struct iocb cb = { .aio_lio_opcode = IOCB_CMD_POLL, .aio_fildes = fd };
struct iocb *cbp = &cb;

sprintf(opts, "fd=%d,rootmode=040000,user_id=0,group_id=0", fd);
mkdir("mnt", 0700);
mount("foo", "mnt", "fuse", 0, opts);
syscall(__NR_io_setup, 1, &ctx);
syscall(__NR_io_submit, ctx, 1, &cbp);
}

Beginning of lockdep output:

=====================================================
WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected

5.3.0-rc5 #9 Not tainted
-----------------------------------------------------
syz_fuse/135 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
000000003590ceda (&fiq->waitq){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
000000003590ceda (&fiq->waitq){+.+.}, at: aio_poll fs/aio.c:1751 [inline]
000000003590ceda (&fiq->waitq){+.+.}, at: __io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825

and this task is already holding:

0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq include/linux/spinlock.h:363 [inline]
0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll fs/aio.c:1749 [inline]
0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one.constprop.0+0x1f4/0x5b0 fs/aio.c:1825

which would create a new lock dependency:
(&(&ctx->ctx_lock)->rlock){..-.} -> (&fiq->waitq){+.+.}

but this new dependency connects a SOFTIRQ-irq-safe lock:
(&(&ctx->ctx_lock)->rlock){..-.}

[...]

Reported-by: syzbot@af05535bb79520f95431@syzkaller.appspotmail.com
Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL")
Cc: <sta...@vger.kernel.org> # v4.19+
Cc: Christoph Hellwig <h...@lst.de>
Signed-off-by: Eric Biggers <ebig...@google.com>
---
fs/fuse/dev.c | 60 ++++++++++++++++++++++++------------------------
fs/fuse/fuse_i.h | 3 ++-
2 files changed, 32 insertions(+), 31 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ea8237513dfa..ef2d8642671e 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -389,7 +389,7 @@ void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,
forget->forget_one.nodeid = nodeid;
forget->forget_one.nlookup = nlookup;

- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
if (fiq->connected) {
fiq->forget_list_tail->next = forget;
fiq->forget_list_tail = forget;
@@ -398,7 +398,7 @@ void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,
} else {
kfree(forget);
}
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
}

static void flush_bg_queue(struct fuse_conn *fc)
@@ -412,10 +412,10 @@ static void flush_bg_queue(struct fuse_conn *fc)
req = list_first_entry(&fc->bg_queue, struct fuse_req, list);
list_del(&req->list);
fc->active_background++;
- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
req->in.h.unique = fuse_get_unique(fiq);
queue_request(fiq, req);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
}
}

@@ -439,9 +439,9 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
* smp_mb() from queue_interrupt().
*/
if (!list_empty(&req->intr_entry)) {
- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
list_del_init(&req->intr_entry);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
}
WARN_ON(test_bit(FR_PENDING, &req->flags));
WARN_ON(test_bit(FR_SENT, &req->flags));
@@ -483,10 +483,10 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)

static int queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
{
- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
/* Check for we've sent request to interrupt this req */
if (unlikely(!test_bit(FR_INTERRUPTED, &req->flags))) {
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
return -EINVAL;
}

@@ -499,13 +499,13 @@ static int queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
smp_mb();
if (test_bit(FR_FINISHED, &req->flags)) {
list_del_init(&req->intr_entry);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
return 0;
}
wake_up_locked(&fiq->waitq);
kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
}
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
return 0;
}

@@ -535,16 +535,16 @@ static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req)
if (!err)
return;

- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
/* Request is not yet in userspace, bail out */
if (test_bit(FR_PENDING, &req->flags)) {
list_del(&req->list);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
__fuse_put_request(req);
req->out.h.error = -EINTR;
return;
}
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
}

/*
@@ -559,9 +559,9 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
struct fuse_iqueue *fiq = &fc->iq;

BUG_ON(test_bit(FR_BACKGROUND, &req->flags));
- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
if (!fiq->connected) {
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
req->out.h.error = -ENOTCONN;
} else {
req->in.h.unique = fuse_get_unique(fiq);
@@ -569,7 +569,7 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
/* acquire extra reference, since request is still needed
after request_end() */
__fuse_get_request(req);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);

request_wait_answer(fc, req);
/* Pairs with smp_wmb() in request_end() */
@@ -700,12 +700,12 @@ static int fuse_request_send_notify_reply(struct fuse_conn *fc,

__clear_bit(FR_ISREPLY, &req->flags);
req->in.h.unique = unique;
- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
if (fiq->connected) {
queue_request(fiq, req);
err = 0;
}
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);

return err;
}
@@ -1169,7 +1169,7 @@ __releases(fiq->waitq.lock)
ih.unique = (req->in.h.unique | FUSE_INT_REQ_BIT);
arg.unique = req->in.h.unique;

- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
if (nbytes < reqsize)
return -EINVAL;

@@ -1220,7 +1220,7 @@ __releases(fiq->waitq.lock)
.len = sizeof(ih) + sizeof(arg),
};

- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
kfree(forget);
if (nbytes < ih.len)
return -EINVAL;
@@ -1252,13 +1252,13 @@ __releases(fiq->waitq.lock)
};

if (nbytes < ih.len) {
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
return -EINVAL;
}

max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one);
head = dequeue_forget(fiq, max_forgets, &count);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);

arg.count = count;
ih.len += count * sizeof(struct fuse_forget_one);
@@ -1318,13 +1318,13 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
unsigned int hash;

restart:
- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
err = -EAGAIN;
if ((file->f_flags & O_NONBLOCK) && fiq->connected &&
!request_pending(fiq))
goto err_unlock;

- err = wait_event_interruptible_exclusive_locked(fiq->waitq,
+ err = wait_event_interruptible_exclusive_locked_irq(fiq->waitq,
!fiq->connected || request_pending(fiq));
if (err)
goto err_unlock;
@@ -1351,7 +1351,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
req = list_entry(fiq->pending.next, struct fuse_req, list);
clear_bit(FR_PENDING, &req->flags);
list_del_init(&req->list);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);

in = &req->in;
reqsize = in->h.len;
@@ -1409,7 +1409,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
return err;

err_unlock:
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
return err;
}

@@ -2121,12 +2121,12 @@ static __poll_t fuse_dev_poll(struct file *file, poll_table *wait)
fiq = &fud->fc->iq;
poll_wait(file, &fiq->waitq, wait);

- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
if (!fiq->connected)
mask = EPOLLERR;
else if (request_pending(fiq))
mask |= EPOLLIN | EPOLLRDNORM;
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);

return mask;
}
@@ -2221,7 +2221,7 @@ void fuse_abort_conn(struct fuse_conn *fc)
flush_bg_queue(fc);
spin_unlock(&fc->bg_lock);

- spin_lock(&fiq->waitq.lock);
+ spin_lock_irq(&fiq->waitq.lock);
fiq->connected = 0;
list_for_each_entry(req, &fiq->pending, list)
clear_bit(FR_PENDING, &req->flags);
@@ -2229,7 +2229,7 @@ void fuse_abort_conn(struct fuse_conn *fc)
while (forget_pending(fiq))
kfree(dequeue_forget(fiq, 1, NULL));
wake_up_all_locked(&fiq->waitq);
- spin_unlock(&fiq->waitq.lock);
+ spin_unlock_irq(&fiq->waitq.lock);
kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
end_polls(fc);
wake_up_all(&fc->blocked_waitq);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 24dbca777775..da31ece761f3 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -450,7 +450,8 @@ struct fuse_iqueue {
/** Connection established */
unsigned connected;

- /** Readers of the connection are waiting on this */
+ /** Readers of the connection are waiting on this. waitq.lock must be
+ taken with spin_lock_irq(), to avoid a deadlock with aio_poll(). */
wait_queue_head_t waitq;

/** The next unique request id */
--
2.22.0

[Miklos Szeredi]

On Fri, Aug 23, 2019 at 1:35 AM Eric Biggers <ebig...@kernel.org> wrote:
>
> From: Eric Biggers <ebig...@google.com>
>
> When IOCB_CMD_POLL is used on the FUSE device, aio_poll() disables IRQs
> and takes kioctx::ctx_lock, then fuse_iqueue::waitq.lock.

Not in -linus.

Which tree was this reproduced with?

Thanks,
Miklos

[Eric Biggers]

Linus's tree. Here's the full symbolized output on v5.3-rc7:

=====================================================
WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected

5.3.0-rc7 #1 Not tainted
-----------------------------------------------------
syz_fuse/150 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
00000000c2701b26 (&fiq->waitq){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
00000000c2701b26 (&fiq->waitq){+.+.}, at: aio_poll fs/aio.c:1751 [inline]
00000000c2701b26 (&fiq->waitq){+.+.}, at: __io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825

and this task is already holding:

00000000f4c02e81 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq include/linux/spinlock.h:363 [inline]
00000000f4c02e81 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll fs/aio.c:1749 [inline]
00000000f4c02e81 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one.constprop.0+0x1f4/0x5b0 fs/aio.c:1825

which would create a new lock dependency:
(&(&ctx->ctx_lock)->rlock){..-.} -> (&fiq->waitq){+.+.}

but this new dependency connects a SOFTIRQ-irq-safe lock:
(&(&ctx->ctx_lock)->rlock){..-.}

... which became SOFTIRQ-irq-safe at:
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
_raw_spin_lock_irq+0x32/0x50 kernel/locking/spinlock.c:167
spin_lock_irq include/linux/spinlock.h:363 [inline]
free_ioctx_users+0x25/0x190 fs/aio.c:618

percpu_ref_put_many include/linux/percpu-refcount.h:293 [inline]
percpu_ref_put include/linux/percpu-refcount.h:309 [inline]
percpu_ref_call_confirm_rcu lib/percpu-refcount.c:130 [inline]

percpu_ref_switch_to_atomic_rcu+0x202/0x210 lib/percpu-refcount.c:165
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch+0x2ae/0x890 kernel/rcu/tree.c:2114
rcu_core+0x13a/0x370 kernel/rcu/tree.c:2314
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2323
__do_softirq+0xbe/0x400 kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x8f/0xc0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:537 [inline]
smp_apic_timer_interrupt+0x8e/0x210 arch/x86/kernel/apic/apic.c:1133
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
default_idle+0x29/0x160 arch/x86/kernel/process.c:580
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:571
default_idle_call+0x1e/0x30 kernel/sched/idle.c:94
cpuidle_idle_call kernel/sched/idle.c:154 [inline]
do_idle+0x1f0/0x220 kernel/sched/idle.c:263
cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:354
rest_init+0x18a/0x24d init/main.c:451
arch_call_rest_init+0x9/0xc
start_kernel+0x530/0x54e init/main.c:785
x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:472
x86_64_start_kernel+0x6d/0x71 arch/x86/kernel/head64.c:453
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241

to a SOFTIRQ-irq-unsafe lock:
(&fiq->waitq){+.+.}

... which became SOFTIRQ-irq-unsafe at:
...

lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x91/0xf0 fs/fuse/dev.c:415
fuse_request_queue_background+0xd1/0x140 fs/fuse/dev.c:676
fuse_request_send_background+0x27/0x60 fs/fuse/dev.c:687
fuse_send_init fs/fuse/inode.c:986 [inline]
fuse_fill_super+0x656/0x681 fs/fuse/inode.c:1211
mount_nodev+0x42/0x90 fs/super.c:1329
fuse_mount+0x13/0x20 fs/fuse/inode.c:1236
legacy_get_tree+0x2c/0x50 fs/fs_context.c:661
vfs_get_tree+0x22/0xc0 fs/super.c:1413
do_new_mount fs/namespace.c:2791 [inline]
do_mount+0x7e3/0xa60 fs/namespace.c:3111
ksys_mount+0x7d/0xd0 fs/namespace.c:3320
__do_sys_mount fs/namespace.c:3334 [inline]
__se_sys_mount fs/namespace.c:3331 [inline]
__x64_sys_mount+0x20/0x30 fs/namespace.c:3331
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296

entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Possible interrupt unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&fiq->waitq);
local_irq_disable();
lock(&(&ctx->ctx_lock)->rlock);
lock(&fiq->waitq);
<Interrupt>
lock(&(&ctx->ctx_lock)->rlock);

*** DEADLOCK ***

1 lock held by syz_fuse/150:
#0: 00000000f4c02e81 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq include/linux/spinlock.h:363 [inline]
#0: 00000000f4c02e81 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll fs/aio.c:1749 [inline]
#0: 00000000f4c02e81 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one.constprop.0+0x1f4/0x5b0 fs/aio.c:1825

the dependencies between SOFTIRQ-irq-safe lock and the holding lock:
-> (&(&ctx->ctx_lock)->rlock){..-.} {
IN-SOFTIRQ-W at:

lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
_raw_spin_lock_irq+0x32/0x50 kernel/locking/spinlock.c:167
spin_lock_irq include/linux/spinlock.h:363 [inline]
free_ioctx_users+0x25/0x190 fs/aio.c:618

percpu_ref_put_many include/linux/percpu-refcount.h:293 [inline]
percpu_ref_put include/linux/percpu-refcount.h:309 [inline]
percpu_ref_call_confirm_rcu lib/percpu-refcount.c:130 [inline]

percpu_ref_switch_to_atomic_rcu+0x202/0x210 lib/percpu-refcount.c:165
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch+0x2ae/0x890 kernel/rcu/tree.c:2114
rcu_core+0x13a/0x370 kernel/rcu/tree.c:2314
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2323
__do_softirq+0xbe/0x400 kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x8f/0xc0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:537 [inline]
smp_apic_timer_interrupt+0x8e/0x210 arch/x86/kernel/apic/apic.c:1133
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
default_idle+0x29/0x160 arch/x86/kernel/process.c:580
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:571
default_idle_call+0x1e/0x30 kernel/sched/idle.c:94
cpuidle_idle_call kernel/sched/idle.c:154 [inline]
do_idle+0x1f0/0x220 kernel/sched/idle.c:263
cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:354
rest_init+0x18a/0x24d init/main.c:451
arch_call_rest_init+0x9/0xc
start_kernel+0x530/0x54e init/main.c:785
x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:472
x86_64_start_kernel+0x6d/0x71 arch/x86/kernel/head64.c:453
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
INITIAL USE at:
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
_raw_spin_lock_irq+0x32/0x50 kernel/locking/spinlock.c:167
spin_lock_irq include/linux/spinlock.h:363 [inline]
free_ioctx_users+0x25/0x190 fs/aio.c:618

percpu_ref_put_many include/linux/percpu-refcount.h:293 [inline]
percpu_ref_put include/linux/percpu-refcount.h:309 [inline]
percpu_ref_call_confirm_rcu lib/percpu-refcount.c:130 [inline]

percpu_ref_switch_to_atomic_rcu+0x202/0x210 lib/percpu-refcount.c:165
__rcu_reclaim kernel/rcu/rcu.h:222 [inline]
rcu_do_batch+0x2ae/0x890 kernel/rcu/tree.c:2114
rcu_core+0x13a/0x370 kernel/rcu/tree.c:2314
rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2323
__do_softirq+0xbe/0x400 kernel/softirq.c:292
invoke_softirq kernel/softirq.c:373 [inline]
irq_exit+0x8f/0xc0 kernel/softirq.c:413
exiting_irq arch/x86/include/asm/apic.h:537 [inline]
smp_apic_timer_interrupt+0x8e/0x210 arch/x86/kernel/apic/apic.c:1133
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
default_idle+0x29/0x160 arch/x86/kernel/process.c:580
arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:571
default_idle_call+0x1e/0x30 kernel/sched/idle.c:94
cpuidle_idle_call kernel/sched/idle.c:154 [inline]
do_idle+0x1f0/0x220 kernel/sched/idle.c:263
cpu_startup_entry+0x1b/0x20 kernel/sched/idle.c:354
rest_init+0x18a/0x24d init/main.c:451
arch_call_rest_init+0x9/0xc
start_kernel+0x530/0x54e init/main.c:785
x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:472
x86_64_start_kernel+0x6d/0x71 arch/x86/kernel/head64.c:453
secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:241
}
... key at: [<ffffffff82860670>] __key.50377+0x0/0x10
... acquired at:
check_prev_add+0xa7/0x950 kernel/locking/lockdep.c:2409
check_prevs_add kernel/locking/lockdep.c:2507 [inline]
validate_chain+0x483/0x870 kernel/locking/lockdep.c:2897
__lock_acquire+0x447/0x7d0 kernel/locking/lockdep.c:3880
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
aio_poll fs/aio.c:1751 [inline]
__io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825
io_submit_one+0x146/0x5b0 fs/aio.c:1862
__do_sys_io_submit fs/aio.c:1921 [inline]
__se_sys_io_submit+0x8e/0x270 fs/aio.c:1891
__x64_sys_io_submit+0x15/0x20 fs/aio.c:1891
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296

entry_SYSCALL_64_after_hwframe+0x49/0xbe


the dependencies between the lock to be acquired
and SOFTIRQ-irq-unsafe lock:
-> (&fiq->waitq){+.+.} {
HARDIRQ-ON-W at:

lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x91/0xf0 fs/fuse/dev.c:415
fuse_request_queue_background+0xd1/0x140 fs/fuse/dev.c:676
fuse_request_send_background+0x27/0x60 fs/fuse/dev.c:687
fuse_send_init fs/fuse/inode.c:986 [inline]
fuse_fill_super+0x656/0x681 fs/fuse/inode.c:1211
mount_nodev+0x42/0x90 fs/super.c:1329
fuse_mount+0x13/0x20 fs/fuse/inode.c:1236
legacy_get_tree+0x2c/0x50 fs/fs_context.c:661
vfs_get_tree+0x22/0xc0 fs/super.c:1413
do_new_mount fs/namespace.c:2791 [inline]
do_mount+0x7e3/0xa60 fs/namespace.c:3111
ksys_mount+0x7d/0xd0 fs/namespace.c:3320
__do_sys_mount fs/namespace.c:3334 [inline]
__se_sys_mount fs/namespace.c:3331 [inline]
__x64_sys_mount+0x20/0x30 fs/namespace.c:3331
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
SOFTIRQ-ON-W at:
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x91/0xf0 fs/fuse/dev.c:415
fuse_request_queue_background+0xd1/0x140 fs/fuse/dev.c:676
fuse_request_send_background+0x27/0x60 fs/fuse/dev.c:687
fuse_send_init fs/fuse/inode.c:986 [inline]
fuse_fill_super+0x656/0x681 fs/fuse/inode.c:1211
mount_nodev+0x42/0x90 fs/super.c:1329
fuse_mount+0x13/0x20 fs/fuse/inode.c:1236
legacy_get_tree+0x2c/0x50 fs/fs_context.c:661
vfs_get_tree+0x22/0xc0 fs/super.c:1413
do_new_mount fs/namespace.c:2791 [inline]
do_mount+0x7e3/0xa60 fs/namespace.c:3111
ksys_mount+0x7d/0xd0 fs/namespace.c:3320
__do_sys_mount fs/namespace.c:3334 [inline]
__se_sys_mount fs/namespace.c:3331 [inline]
__x64_sys_mount+0x20/0x30 fs/namespace.c:3331
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
INITIAL USE at:
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
flush_bg_queue+0x91/0xf0 fs/fuse/dev.c:415
fuse_request_queue_background+0xd1/0x140 fs/fuse/dev.c:676
fuse_request_send_background+0x27/0x60 fs/fuse/dev.c:687
fuse_send_init fs/fuse/inode.c:986 [inline]
fuse_fill_super+0x656/0x681 fs/fuse/inode.c:1211
mount_nodev+0x42/0x90 fs/super.c:1329
fuse_mount+0x13/0x20 fs/fuse/inode.c:1236
legacy_get_tree+0x2c/0x50 fs/fs_context.c:661
vfs_get_tree+0x22/0xc0 fs/super.c:1413
do_new_mount fs/namespace.c:2791 [inline]
do_mount+0x7e3/0xa60 fs/namespace.c:3111
ksys_mount+0x7d/0xd0 fs/namespace.c:3320
__do_sys_mount fs/namespace.c:3334 [inline]
__se_sys_mount fs/namespace.c:3331 [inline]
__x64_sys_mount+0x20/0x30 fs/namespace.c:3331
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
}
... key at: [<ffffffff82863ea0>] __key.40870+0x0/0x10
... acquired at:
check_prev_add+0xa7/0x950 kernel/locking/lockdep.c:2409
check_prevs_add kernel/locking/lockdep.c:2507 [inline]
validate_chain+0x483/0x870 kernel/locking/lockdep.c:2897
__lock_acquire+0x447/0x7d0 kernel/locking/lockdep.c:3880
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
aio_poll fs/aio.c:1751 [inline]
__io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825
io_submit_one+0x146/0x5b0 fs/aio.c:1862
__do_sys_io_submit fs/aio.c:1921 [inline]
__se_sys_io_submit+0x8e/0x270 fs/aio.c:1891
__x64_sys_io_submit+0x15/0x20 fs/aio.c:1891
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe


stack backtrace:
CPU: 1 PID: 150 Comm: syz_fuse Not tainted 5.3.0-rc7 #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014

Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]

dump_stack+0x70/0x9a lib/dump_stack.c:113
print_bad_irq_dependency.cold+0x380/0x3d8 kernel/locking/lockdep.c:2025
check_irq_usage+0x337/0x400 kernel/locking/lockdep.c:2223
check_prev_add+0xa7/0x950 kernel/locking/lockdep.c:2409
check_prevs_add kernel/locking/lockdep.c:2507 [inline]
validate_chain+0x483/0x870 kernel/locking/lockdep.c:2897
__lock_acquire+0x447/0x7d0 kernel/locking/lockdep.c:3880
lock_acquire+0x99/0x180 kernel/locking/lockdep.c:4412
__raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_lock+0x2b/0x40 kernel/locking/spinlock.c:151
spin_lock include/linux/spinlock.h:338 [inline]
aio_poll fs/aio.c:1751 [inline]
__io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825
io_submit_one+0x146/0x5b0 fs/aio.c:1862
__do_sys_io_submit fs/aio.c:1921 [inline]
__se_sys_io_submit+0x8e/0x270 fs/aio.c:1891
__x64_sys_io_submit+0x15/0x20 fs/aio.c:1891
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f1bbde7ec6d
Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d f3 51 0c 00 f7 d8 64 89 01 48
RSP: 002b:00007ffffa3a70e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 00007ffffa3a7140 RCX: 00007f1bbde7ec6d
RDX: 00007ffffa3a70f8 RSI: 0000000000000001 RDI: 00007f1bbe27d000
RBP: 0000559337c29290 R08: 0000000000000000 R09: 00007f1bbe27d000
R10: 0000000000000029 R11: 0000000000000246 R12: 0000559337c29190
R13: 00007ffffa3a72b0 R14: 0000000000000000 R15: 0000000000000000

[Miklos Szeredi]

On Tue, Sep 3, 2019 at 3:39 PM Eric Biggers <ebig...@kernel.org> wrote:
>
> On Tue, Sep 03, 2019 at 09:31:29AM +0200, Miklos Szeredi wrote:
> > On Fri, Aug 23, 2019 at 1:35 AM Eric Biggers <ebig...@kernel.org> wrote:
> > >
> > > From: Eric Biggers <ebig...@google.com>
> > >
> > > When IOCB_CMD_POLL is used on the FUSE device, aio_poll() disables IRQs
> > > and takes kioctx::ctx_lock, then fuse_iqueue::waitq.lock.
> >
> > Not in -linus.
> >
> > Which tree was this reproduced with?
> >
> > Thanks,
> > Miklos
>
> Linus's tree. Here's the full symbolized output on v5.3-rc7:

Okay.

TBH, I find the fix disgusting. It's confusing to sprinke code that
has absolutely nothing to do with interrupts with spin_lock_irq()
calls.

I think the lock/unlock calls should at least be done with a helper
with a comment explaining why disabling interrupts is needed (though I
have not managed to understand why aio needs to actually mess with the
waitq lock...)

Probably a better fix would be to just use a separate spinlock to
avoid the need to disable interrupts in cases where it's not
necessary.

Thanks,
Miklos

[Eric Biggers]

On Wed, Sep 04, 2019 at 04:29:03PM +0200, Miklos Szeredi wrote:
> On Tue, Sep 3, 2019 at 3:39 PM Eric Biggers <ebig...@kernel.org> wrote:
> >
> > On Tue, Sep 03, 2019 at 09:31:29AM +0200, Miklos Szeredi wrote:
> > > On Fri, Aug 23, 2019 at 1:35 AM Eric Biggers <ebig...@kernel.org> wrote:
> > > >
> > > > From: Eric Biggers <ebig...@google.com>
> > > >
> > > > When IOCB_CMD_POLL is used on the FUSE device, aio_poll() disables IRQs
> > > > and takes kioctx::ctx_lock, then fuse_iqueue::waitq.lock.
> > >
> > > Not in -linus.
> > >
> > > Which tree was this reproduced with?
> > >
> > > Thanks,
> > > Miklos
> >
> > Linus's tree. Here's the full symbolized output on v5.3-rc7:
>
> Okay.
>
> TBH, I find the fix disgusting. It's confusing to sprinke code that
> has absolutely nothing to do with interrupts with spin_lock_irq()
> calls.
>
> I think the lock/unlock calls should at least be done with a helper
> with a comment explaining why disabling interrupts is needed (though I
> have not managed to understand why aio needs to actually mess with the
> waitq lock...)

The aio code is doing a poll(), so it needs to use the wait queue.

>
> Probably a better fix would be to just use a separate spinlock to
> avoid the need to disable interrupts in cases where it's not
> necessary.

Well, the below is what a separate lock would look like. Note that it actually
still disables IRQs in some places; it's just hidden away in the nested
spin_lock_irqsave() in wake_up(). Likewise, adding something to the fuse_iqueue
then requires taking 2 spin locks -- one explicit, and one hidden in wake_up().

Is this the solution you'd prefer?

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ea8237513dfa..1d9d555f2699 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -377,7 +377,7 @@ static void queue_request(struct fuse_iqueue *fiq, struct fuse_req *req)
req->in.h.len = sizeof(struct fuse_in_header) +
len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
list_add_tail(&req->list, &fiq->pending);
- wake_up_locked(&fiq->waitq);
+ wake_up(&fiq->waitq);
kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
}

@@ -389,16 +389,16 @@ void fuse_queue_forget(struct fuse_conn *fc, struct fuse_forget_link *forget,

forget->forget_one.nodeid = nodeid;
forget->forget_one.nlookup = nlookup;

- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

if (fiq->connected) {
fiq->forget_list_tail->next = forget;
fiq->forget_list_tail = forget;

- wake_up_locked(&fiq->waitq);
+ wake_up(&fiq->waitq);
kill_fasync(&fiq->fasync, SIGIO, POLL_IN);

} else {
kfree(forget);
}
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

}

static void flush_bg_queue(struct fuse_conn *fc)
@@ -412,10 +412,10 @@ static void flush_bg_queue(struct fuse_conn *fc)
req = list_first_entry(&fc->bg_queue, struct fuse_req, list);
list_del(&req->list);
fc->active_background++;
- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

req->in.h.unique = fuse_get_unique(fiq);
queue_request(fiq, req);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

}
}

@@ -439,9 +439,9 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)
* smp_mb() from queue_interrupt().
*/
if (!list_empty(&req->intr_entry)) {
- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

list_del_init(&req->intr_entry);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

}
WARN_ON(test_bit(FR_PENDING, &req->flags));
WARN_ON(test_bit(FR_SENT, &req->flags));
@@ -483,10 +483,10 @@ static void request_end(struct fuse_conn *fc, struct fuse_req *req)

static int queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
{
- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

/* Check for we've sent request to interrupt this req */
if (unlikely(!test_bit(FR_INTERRUPTED, &req->flags))) {
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

return -EINVAL;
}

@@ -499,13 +499,13 @@ static int queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
smp_mb();
if (test_bit(FR_FINISHED, &req->flags)) {
list_del_init(&req->intr_entry);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);
return 0;
}
- wake_up_locked(&fiq->waitq);
+ wake_up(&fiq->waitq);

kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
}
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

return 0;
}

@@ -535,16 +535,16 @@ static void request_wait_answer(struct fuse_conn *fc, struct fuse_req *req)
if (!err)
return;

- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

/* Request is not yet in userspace, bail out */
if (test_bit(FR_PENDING, &req->flags)) {
list_del(&req->list);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);;

__fuse_put_request(req);
req->out.h.error = -EINTR;
return;
}
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

}

/*
@@ -559,9 +559,9 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
struct fuse_iqueue *fiq = &fc->iq;

BUG_ON(test_bit(FR_BACKGROUND, &req->flags));
- spin_lock(&fiq->waitq.lock);

+ spin_lock_irq(&fiq->lock);

if (!fiq->connected) {
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

req->out.h.error = -ENOTCONN;
} else {
req->in.h.unique = fuse_get_unique(fiq);
@@ -569,7 +569,7 @@ static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
/* acquire extra reference, since request is still needed
after request_end() */
__fuse_get_request(req);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

request_wait_answer(fc, req);
/* Pairs with smp_wmb() in request_end() */
@@ -700,12 +700,12 @@ static int fuse_request_send_notify_reply(struct fuse_conn *fc,

__clear_bit(FR_ISREPLY, &req->flags);
req->in.h.unique = unique;
- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

if (fiq->connected) {
queue_request(fiq, req);
err = 0;
}
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

return err;
}
@@ -1149,12 +1149,12 @@ static int request_pending(struct fuse_iqueue *fiq)
* Unlike other requests this is assembled on demand, without a need
* to allocate a separate fuse_req structure.
*
- * Called with fiq->waitq.lock held, releases it
+ * Called with fiq->lock held, releases it
*/
static int fuse_read_interrupt(struct fuse_iqueue *fiq,
struct fuse_copy_state *cs,
size_t nbytes, struct fuse_req *req)
-__releases(fiq->waitq.lock)
+__releases(fiq->lock)
{
struct fuse_in_header ih;
struct fuse_interrupt_in arg;

@@ -1169,7 +1169,7 @@ __releases(fiq->waitq.lock)
ih.unique = (req->in.h.unique | FUSE_INT_REQ_BIT);
arg.unique = req->in.h.unique;

- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

if (nbytes < reqsize)
return -EINVAL;

@@ -1206,7 +1206,7 @@ static struct fuse_forget_link *dequeue_forget(struct fuse_iqueue *fiq,
static int fuse_read_single_forget(struct fuse_iqueue *fiq,
struct fuse_copy_state *cs,
size_t nbytes)
-__releases(fiq->waitq.lock)
+__releases(fiq->lock)
{
int err;
struct fuse_forget_link *forget = dequeue_forget(fiq, 1, NULL);

@@ -1220,7 +1220,7 @@ __releases(fiq->waitq.lock)
.len = sizeof(ih) + sizeof(arg),
};

- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

kfree(forget);
if (nbytes < ih.len)
return -EINVAL;

@@ -1238,7 +1238,7 @@ __releases(fiq->waitq.lock)

static int fuse_read_batch_forget(struct fuse_iqueue *fiq,
struct fuse_copy_state *cs, size_t nbytes)
-__releases(fiq->waitq.lock)
+__releases(fiq->lock)
{
int err;
unsigned max_forgets;

@@ -1252,13 +1252,13 @@ __releases(fiq->waitq.lock)
};

if (nbytes < ih.len) {
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

return -EINVAL;
}

max_forgets = (nbytes - ih.len) / sizeof(struct fuse_forget_one);
head = dequeue_forget(fiq, max_forgets, &count);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

arg.count = count;
ih.len += count * sizeof(struct fuse_forget_one);

@@ -1288,7 +1288,7 @@ __releases(fiq->waitq.lock)
static int fuse_read_forget(struct fuse_conn *fc, struct fuse_iqueue *fiq,
struct fuse_copy_state *cs,
size_t nbytes)
-__releases(fiq->waitq.lock)
+__releases(fiq->lock)
{
if (fc->minor < 16 || fiq->forget_list_head.next->next == NULL)
return fuse_read_single_forget(fiq, cs, nbytes);
@@ -1318,16 +1318,19 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,

unsigned int hash;

restart:
- spin_lock(&fiq->waitq.lock);

- err = -EAGAIN;
- if ((file->f_flags & O_NONBLOCK) && fiq->connected &&
- !request_pending(fiq))
- goto err_unlock;
+ for (;;) {
+ spin_lock(&fiq->lock);
+ if (!fiq->connected || request_pending(fiq))
+ break;
+ spin_unlock(&fiq->lock);

- err = wait_event_interruptible_exclusive_locked(fiq->waitq,

+ if (file->f_flags & O_NONBLOCK)
+ return -EAGAIN;
+ err = wait_event_interruptible_exclusive(fiq->waitq,
!fiq->connected || request_pending(fiq));
- if (err)
- goto err_unlock;
+ if (err)
+ return err;
+ }

if (!fiq->connected) {
err = fc->aborted ? -ECONNABORTED : -ENODEV;
@@ -1351,7 +1354,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,

req = list_entry(fiq->pending.next, struct fuse_req, list);
clear_bit(FR_PENDING, &req->flags);
list_del_init(&req->list);
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

in = &req->in;
reqsize = in->h.len;

@@ -1409,7 +1412,7 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,

return err;

err_unlock:
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);
return err;
}

@@ -2121,12 +2124,12 @@ static __poll_t fuse_dev_poll(struct file *file, poll_table *wait)

fiq = &fud->fc->iq;
poll_wait(file, &fiq->waitq, wait);

- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

if (!fiq->connected)
mask = EPOLLERR;
else if (request_pending(fiq))
mask |= EPOLLIN | EPOLLRDNORM;
- spin_unlock(&fiq->waitq.lock);

+ spin_unlock(&fiq->lock);

return mask;
}
@@ -2221,15 +2224,15 @@ void fuse_abort_conn(struct fuse_conn *fc)

flush_bg_queue(fc);
spin_unlock(&fc->bg_lock);

- spin_lock(&fiq->waitq.lock);

+ spin_lock(&fiq->lock);

fiq->connected = 0;
list_for_each_entry(req, &fiq->pending, list)
clear_bit(FR_PENDING, &req->flags);

list_splice_tail_init(&fiq->pending, &to_end);

while (forget_pending(fiq))
kfree(dequeue_forget(fiq, 1, NULL));

- wake_up_all_locked(&fiq->waitq);
- spin_unlock(&fiq->waitq.lock);
+ wake_up_all(&fiq->waitq);
+ spin_unlock(&fiq->lock);

kill_fasync(&fiq->fasync, SIGIO, POLL_IN);
end_polls(fc);
wake_up_all(&fc->blocked_waitq);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h

index 24dbca777775..5de7fd0fd6ef 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -450,6 +450,9 @@ struct fuse_iqueue {

/** Connection established */
unsigned connected;

+ /** Lock protecting accessess to members of this structure */
+ spinlock_t lock;
+
/** Readers of the connection are waiting on this */
wait_queue_head_t waitq;

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 4bb885b0f032..987877860c01 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -582,6 +582,7 @@ static int fuse_show_options(struct seq_file *m, struct dentry *root)
static void fuse_iqueue_init(struct fuse_iqueue *fiq)
{
memset(fiq, 0, sizeof(struct fuse_iqueue));
+ spin_lock_init(&fiq->lock);
init_waitqueue_head(&fiq->waitq);
INIT_LIST_HEAD(&fiq->pending);
INIT_LIST_HEAD(&fiq->interrupts);
--
2.23.0

[Miklos Szeredi]

On Fri, Sep 6, 2019 at 6:43 AM Eric Biggers <ebig...@kernel.org> wrote:
>
> On Wed, Sep 04, 2019 at 04:29:03PM +0200, Miklos Szeredi wrote:

> > TBH, I find the fix disgusting. It's confusing to sprinke code that
> > has absolutely nothing to do with interrupts with spin_lock_irq()
> > calls.
> >
> > I think the lock/unlock calls should at least be done with a helper
> > with a comment explaining why disabling interrupts is needed (though I
> > have not managed to understand why aio needs to actually mess with the
> > waitq lock...)
>
> The aio code is doing a poll(), so it needs to use the wait queue.

Doesn't explain why the irq disabled nested locking is needed in
aio_poll(). poll/select manage to do that without messing with waitq
internals. How is aio poll different?

> >
> > Probably a better fix would be to just use a separate spinlock to
> > avoid the need to disable interrupts in cases where it's not
> > necessary.
>
> Well, the below is what a separate lock would look like. Note that it actually
> still disables IRQs in some places; it's just hidden away in the nested
> spin_lock_irqsave() in wake_up(). Likewise, adding something to the fuse_iqueue
> then requires taking 2 spin locks -- one explicit, and one hidden in wake_up().

Right, that's exactly why the waitq lock was used.

> Is this the solution you'd prefer?

I'd actually prefer if aio was fixed. But I guess that's not
realistic, so yes, the below patch looks okay. If fiq->lock is in the
same cacheline as fiq->waitq then it shouldn't make a difference.

Thanks,
Miklos

[Eric Biggers]

From: Eric Biggers <ebig...@google.com>

When IOCB_CMD_POLL is used on the FUSE device, aio_poll() disables IRQs
and takes kioctx::ctx_lock, then fuse_iqueue::waitq.lock.

This may have to wait for fuse_iqueue::waitq.lock to be released by one
of many places that take it with IRQs enabled. Since the IRQ handler
may take kioctx::ctx_lock, lockdep reports that a deadlock is possible.

Fix it by protecting the state of struct fuse_iqueue with a separate
spinlock, and only accessing fuse_iqueue::waitq using the versions of
the waitqueue functions which do IRQ-safe locking internally.

Reproducer:

#include <fcntl.h>
#include <stdio.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <linux/aio_abi.h>

int main()
{
char opts[128];
int fd = open("/dev/fuse", O_RDWR);
aio_context_t ctx = 0;
struct iocb cb = { .aio_lio_opcode = IOCB_CMD_POLL, .aio_fildes = fd };
struct iocb *cbp = &cb;

sprintf(opts, "fd=%d,rootmode=040000,user_id=0,group_id=0", fd);
mkdir("mnt", 0700);
mount("foo", "mnt", "fuse", 0, opts);
syscall(__NR_io_setup, 1, &ctx);
syscall(__NR_io_submit, ctx, 1, &cbp);
}

Beginning of lockdep output:

=====================================================
WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected

5.3.0-rc5 #9 Not tainted
-----------------------------------------------------

syz_fuse/135 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
000000003590ceda (&fiq->waitq){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
000000003590ceda (&fiq->waitq){+.+.}, at: aio_poll fs/aio.c:1751 [inline]
000000003590ceda (&fiq->waitq){+.+.}, at: __io_submit_one.constprop.0+0x203/0x5b0 fs/aio.c:1825

and this task is already holding:

0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: spin_lock_irq include/linux/spinlock.h:363 [inline]
0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: aio_poll fs/aio.c:1749 [inline]
0000000075037284 (&(&ctx->ctx_lock)->rlock){..-.}, at: __io_submit_one.constprop.0+0x1f4/0x5b0 fs/aio.c:1825

which would create a new lock dependency:
(&(&ctx->ctx_lock)->rlock){..-.} -> (&fiq->waitq){+.+.}

but this new dependency connects a SOFTIRQ-irq-safe lock:
(&(&ctx->ctx_lock)->rlock){..-.}

[...]

Reported-by: syzbot+af0553...@syzkaller.appspotmail.com
Reported-by: syzbot+d86c44...@syzkaller.appspotmail.com

Fixes: bfe4037e722e ("aio: implement IOCB_CMD_POLL")
Cc: <sta...@vger.kernel.org> # v4.19+
Cc: Christoph Hellwig <h...@lst.de>
Signed-off-by: Eric Biggers <ebig...@google.com>
---

fs/fuse/dev.c | 93 +++++++++++++++++++++++++-----------------------
fs/fuse/fuse_i.h | 3 ++
fs/fuse/inode.c | 1 +
3 files changed, 52 insertions(+), 45 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index ea8237513dfa..186468fba82e 100644

index 24dbca777775..89bdc41e0d86 100644

--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -450,6 +450,9 @@ struct fuse_iqueue {
/** Connection established */
unsigned connected;

+ /** Lock protecting accesses to members of this structure */