possible deadlock in seq_read (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e3a56aaade89 Linux 4.14.277
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=152f3b22f00000
kernel config: https://syzkaller.appspot.com/x/.config?x=24efab1c7c06be56
dashboard link: https://syzkaller.appspot.com/bug?extid=eb2fac11ac7c4db9bf49
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+eb2fac...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
4.14.277-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.1/13919 is trying to acquire lock:
(&p->lock){+.+.}, at: [<ffffffff818ef6ea>] seq_read+0xba/0x1180 fs/seq_file.c:168

but task is already holding lock:
(sb_writers#3){.+.+}, at: [<ffffffff8186e50f>] file_start_write include/linux/fs.h:2714 [inline]
(sb_writers#3){.+.+}, at: [<ffffffff8186e50f>] do_sendfile+0x84f/0xb30 fs/read_write.c:1440

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (sb_writers#3){.+.+}:
percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
__sb_start_write+0x64/0x260 fs/super.c:1342
sb_start_write include/linux/fs.h:1551 [inline]
mnt_want_write+0x3a/0xb0 fs/namespace.c:386
ovl_do_remove+0x67/0xb90 fs/overlayfs/dir.c:759
vfs_rmdir.part.0+0x144/0x390 fs/namei.c:3908
vfs_rmdir fs/namei.c:3893 [inline]
do_rmdir+0x334/0x3c0 fs/namei.c:3968
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #2 (&ovl_i_mutex_dir_key[depth]){++++}:
down_read+0x36/0x80 kernel/locking/rwsem.c:24
inode_lock_shared include/linux/fs.h:729 [inline]
do_last fs/namei.c:3333 [inline]
path_openat+0x149b/0x2970 fs/namei.c:3569
do_filp_open+0x179/0x3c0 fs/namei.c:3603
do_open_execat+0xd3/0x450 fs/exec.c:849
do_execveat_common+0x711/0x1f30 fs/exec.c:1755
do_execve fs/exec.c:1860 [inline]
SYSC_execve fs/exec.c:1941 [inline]
SyS_execve+0x3b/0x50 fs/exec.c:1936
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #1 (&sig->cred_guard_mutex){+.+.}:
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
do_io_accounting fs/proc/base.c:2738 [inline]
proc_tgid_io_accounting+0x1b9/0x7a0 fs/proc/base.c:2787
proc_single_show+0xe7/0x150 fs/proc/base.c:761
seq_read+0x4e4/0x1180 fs/seq_file.c:240
do_loop_readv_writev fs/read_write.c:695 [inline]
do_loop_readv_writev fs/read_write.c:682 [inline]
do_iter_read+0x3eb/0x5b0 fs/read_write.c:919
vfs_readv+0xc8/0x120 fs/read_write.c:981
do_preadv fs/read_write.c:1065 [inline]
SYSC_preadv fs/read_write.c:1115 [inline]
SyS_preadv+0x15a/0x200 fs/read_write.c:1110
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #0 (&p->lock){+.+.}:
lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
seq_read+0xba/0x1180 fs/seq_file.c:168
proc_reg_read+0xee/0x1a0 fs/proc/inode.c:217
do_loop_readv_writev fs/read_write.c:695 [inline]
do_loop_readv_writev fs/read_write.c:682 [inline]
do_iter_read+0x3eb/0x5b0 fs/read_write.c:919
vfs_readv+0xc8/0x120 fs/read_write.c:981
kernel_readv fs/splice.c:361 [inline]
default_file_splice_read+0x418/0x910 fs/splice.c:416
do_splice_to+0xfb/0x140 fs/splice.c:880
splice_direct_to_actor+0x207/0x730 fs/splice.c:952
do_splice_direct+0x164/0x210 fs/splice.c:1061
do_sendfile+0x47f/0xb30 fs/read_write.c:1441
SYSC_sendfile64 fs/read_write.c:1502 [inline]
SyS_sendfile64+0xff/0x110 fs/read_write.c:1488
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb

other info that might help us debug this:

Chain exists of:
&p->lock --> &ovl_i_mutex_dir_key[depth] --> sb_writers#3

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(sb_writers#3);
lock(&ovl_i_mutex_dir_key[depth]);
lock(sb_writers#3);
lock(&p->lock);

*** DEADLOCK ***

1 lock held by syz-executor.1/13919:
#0: (sb_writers#3){.+.+}, at: [<ffffffff8186e50f>] file_start_write include/linux/fs.h:2714 [inline]
#0: (sb_writers#3){.+.+}, at: [<ffffffff8186e50f>] do_sendfile+0x84f/0xb30 fs/read_write.c:1440

stack backtrace:
CPU: 0 PID: 13919 Comm: syz-executor.1 Not tainted 4.14.277-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x281 lib/dump_stack.c:58
print_circular_bug.constprop.0.cold+0x2d7/0x41e kernel/locking/lockdep.c:1258
check_prev_add kernel/locking/lockdep.c:1905 [inline]
check_prevs_add kernel/locking/lockdep.c:2022 [inline]
validate_chain kernel/locking/lockdep.c:2464 [inline]
__lock_acquire+0x2e0e/0x3f20 kernel/locking/lockdep.c:3491
lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
seq_read+0xba/0x1180 fs/seq_file.c:168
proc_reg_read+0xee/0x1a0 fs/proc/inode.c:217
do_loop_readv_writev fs/read_write.c:695 [inline]
do_loop_readv_writev fs/read_write.c:682 [inline]
do_iter_read+0x3eb/0x5b0 fs/read_write.c:919
vfs_readv+0xc8/0x120 fs/read_write.c:981
kernel_readv fs/splice.c:361 [inline]
default_file_splice_read+0x418/0x910 fs/splice.c:416
do_splice_to+0xfb/0x140 fs/splice.c:880
splice_direct_to_actor+0x207/0x730 fs/splice.c:952
do_splice_direct+0x164/0x210 fs/splice.c:1061
do_sendfile+0x47f/0xb30 fs/read_write.c:1441
SYSC_sendfile64 fs/read_write.c:1502 [inline]
SyS_sendfile64+0xff/0x110 fs/read_write.c:1488
do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f0d0cbb80e9
RSP: 002b:00007f0d0b52d168 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f0d0cccaf60 RCX: 00007f0d0cbb80e9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00007f0d0cc1208d R08: 0000000000000000 R09: 0000000000000000
R10: 4000000000010046 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe42448e6f R14: 00007f0d0b52d300 R15: 0000000000022000
overlayfs: fs on 'file0' does not support file handles, falling back to index=off.
overlayfs: missing 'lowerdir'
overlayfs: fs on './file0' does not support file handles, falling back to index=off.
overlayfs: unrecognized mount option "obj_role=[(" or missing value
gfs2: gfs2 mount does not exist
overlayfs: fs on 'file0' does not support file handles, falling back to index=off.
overlayfs: missing 'lowerdir'
kauditd_printk_skb: 3 callbacks suppressed
audit: type=1800 audit(1651682687.775:36): pid=14001 uid=0 auid=4294967295 ses=4294967295 op="collect_data" cause="failed(directio)" comm="syz-executor.0" name="bus" dev="sda1" ino=14307 res=0
overlayfs: fs on './file0' does not support file handles, falling back to index=off.
overlayfs: fs on 'file0' does not support file handles, falling back to index=off.
overlayfs: unrecognized mount option "obj_role=[(" or missing value
overlayfs: fs on 'file0' does not support file handles, falling back to index=off.
overlayfs: missing 'lowerdir'
overlayfs: missing 'lowerdir'
overlayfs: fs on './file0' does not support file handles, falling back to index=off.
overlayfs: fs on './file0' does not support file handles, falling back to index=off.
overlayfs: unrecognized mount option "obj_role=[(" or missing value
overlayfs: unrecognized mount option "obj_role=[(" or missing value
gfs2: gfs2 mount does not exist
overlayfs: fs on 'file0' does not support file handles, falling back to index=off.
overlayfs: missing 'lowerdir'
overlayfs: fs on './file0' does not support file handles, falling back to index=off.
overlayfs: unrecognized mount option "obj_role=[(" or missing value
audit: type=1800 audit(1651682688.675:37): pid=14084 uid=0 auid=4294967295 ses=4294967295 op="collect_data" cause="failed(directio)" comm="syz-executor.0" name="bus" dev="sda1" ino=14295 res=0
gfs2: gfs2 mount does not exist
EXT4-fs (loop5): Unrecognized mount option "Z" or missing value
audit: type=1800 audit(1651682688.815:38): pid=14108 uid=0 auid=4294967295 ses=4294967295 op="collect_data" cause="failed(directio)" comm="syz-executor.0" name="bus" dev="sda1" ino=14309 res=0
EXT4-fs (loop5): Unrecognized mount option "Z" or missing value
EXT4-fs (loop5): Unrecognized mount option "Z" or missing value
EXT4-fs (loop0): Unrecognized mount option "Z" or missing value
print_req_error: I/O error, dev loop0, sector 0
Zero length message leads to an empty skb
bridge0: port 3(team0) entered blocking state
bridge0: port 3(team0) entered disabled state
device team0 entered promiscuous mode
device team_slave_0 entered promiscuous mode
device team_slave_1 entered promiscuous mode
device ipvlan1 entered promiscuous mode
bridge0: port 3(team0) entered blocking state
bridge0: port 3(team0) entered forwarding state
bridge0: port 3(team0) entered blocking state
bridge0: port 3(team0) entered disabled state
device team0 entered promiscuous mode
device team_slave_0 entered promiscuous mode
device team_slave_1 entered promiscuous mode
bridge0: port 3(team0) entered blocking state
bridge0: port 3(team0) entered forwarding state
print_req_error: I/O error, dev loop0, sector 0
unregister_netdevice: waiting for ip6gre0 to become free. Usage count = -1


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.