[syzbot] [kernfs?] possible deadlock in __kernfs_remove

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 626737a5791b Merge tag 'pinctrl-v6.10-2' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=143a383e980000
kernel config: https://syzkaller.appspot.com/x/.config?x=d6b9ee98d841760c
dashboard link: https://syzkaller.appspot.com/bug?extid=4762dd74e32532cda5ff
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-626737a5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1cffeb16f347/vmlinux-626737a5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b20910e32f0e/bzImage-626737a5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4762dd...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.10.0-rc5-syzkaller-00012-g626737a5791b #0 Not tainted
------------------------------------------------------
udevd/6164 is trying to acquire lock:
ffff88801d0ffe18 (kn->active#5){++++}-{0:0}, at: __kernfs_remove+0x281/0x670 fs/kernfs/dir.c:1486

but task is already holding lock:
ffff888022a504c8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_release+0x166/0x6f0 block/bdev.c:1080

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&disk->open_mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x175/0x9c0 kernel/locking/mutex.c:752
bdev_open+0x41a/0xe50 block/bdev.c:897
bdev_file_open_by_dev block/bdev.c:1011 [inline]
bdev_file_open_by_dev+0x17d/0x210 block/bdev.c:986
disk_scan_partitions+0x1ed/0x320 block/genhd.c:367
device_add_disk+0xe97/0x1250 block/genhd.c:510
pmem_attach_disk+0x9fe/0x1400 drivers/nvdimm/pmem.c:578
nd_pmem_probe+0x1a9/0x1f0 drivers/nvdimm/pmem.c:651
nvdimm_bus_probe+0x169/0x5d0 drivers/nvdimm/bus.c:91
call_driver_probe drivers/base/dd.c:578 [inline]
really_probe+0x23e/0xa90 drivers/base/dd.c:656
__driver_probe_device+0x1de/0x440 drivers/base/dd.c:798
driver_probe_device+0x4c/0x1b0 drivers/base/dd.c:828
__driver_attach+0x283/0x580 drivers/base/dd.c:1214
bus_for_each_dev+0x13c/0x1d0 drivers/base/bus.c:368
bus_add_driver+0x2e9/0x690 drivers/base/bus.c:673
driver_register+0x15c/0x4b0 drivers/base/driver.c:246
__nd_driver_register+0x103/0x1a0 drivers/nvdimm/bus.c:619
do_one_initcall+0x128/0x700 init/main.c:1267
do_initcall_level init/main.c:1329 [inline]
do_initcalls init/main.c:1345 [inline]
do_basic_setup init/main.c:1364 [inline]
kernel_init_freeable+0x69d/0xca0 init/main.c:1578
kernel_init+0x1c/0x2b0 init/main.c:1467
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #1 (&nvdimm_namespace_key){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x175/0x9c0 kernel/locking/mutex.c:752
device_lock include/linux/device.h:1009 [inline]
uevent_show+0x188/0x3b0 drivers/base/core.c:2743
dev_attr_show+0x53/0xe0 drivers/base/core.c:2437
sysfs_kf_seq_show+0x23e/0x410 fs/sysfs/file.c:59
seq_read_iter+0x4fa/0x12c0 fs/seq_file.c:230
kernfs_fop_read_iter+0x41a/0x590 fs/kernfs/file.c:279
new_sync_read fs/read_write.c:395 [inline]
vfs_read+0x869/0xbd0 fs/read_write.c:476
ksys_read+0x12f/0x260 fs/read_write.c:619
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (kn->active#5){++++}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2478/0x3b30 kernel/locking/lockdep.c:5137
lock_acquire kernel/locking/lockdep.c:5754 [inline]
lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5719
kernfs_drain+0x48f/0x590 fs/kernfs/dir.c:500
__kernfs_remove+0x281/0x670 fs/kernfs/dir.c:1486
kernfs_remove_by_name_ns+0xb2/0x130 fs/kernfs/dir.c:1694
sysfs_remove_file include/linux/sysfs.h:773 [inline]
device_remove_file drivers/base/core.c:3061 [inline]
device_remove_file drivers/base/core.c:3057 [inline]
device_del+0x381/0x9f0 drivers/base/core.c:3866
drop_partition+0x109/0x1c0 block/partitions/core.c:273
bdev_disk_changed+0x24d/0x14f0 block/partitions/core.c:664
__loop_clr_fd+0x392/0x850 drivers/block/loop.c:1208
lo_release+0x188/0x1c0 drivers/block/loop.c:1758
blkdev_put_whole+0xad/0xf0 block/bdev.c:673
bdev_release+0x496/0x6f0 block/bdev.c:1096
blkdev_release+0x15/0x20 block/fops.c:623
__fput+0x408/0xbb0 fs/file_table.c:422
__fput_sync+0x47/0x50 fs/file_table.c:507
__do_sys_close fs/open.c:1555 [inline]
__se_sys_close fs/open.c:1540 [inline]
__x64_sys_close+0x86/0x100 fs/open.c:1540
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
kn->active#5 --> &nvdimm_namespace_key --> &disk->open_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&disk->open_mutex);
lock(&nvdimm_namespace_key);
lock(&disk->open_mutex);
lock(kn->active#5);

*** DEADLOCK ***

1 lock held by udevd/6164:
#0: ffff888022a504c8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_release+0x166/0x6f0 block/bdev.c:1080

stack backtrace:
CPU: 1 PID: 6164 Comm: udevd Not tainted 6.10.0-rc5-syzkaller-00012-g626737a5791b #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114
check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2478/0x3b30 kernel/locking/lockdep.c:5137
lock_acquire kernel/locking/lockdep.c:5754 [inline]
lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5719
kernfs_drain+0x48f/0x590 fs/kernfs/dir.c:500
__kernfs_remove+0x281/0x670 fs/kernfs/dir.c:1486
kernfs_remove_by_name_ns+0xb2/0x130 fs/kernfs/dir.c:1694
sysfs_remove_file include/linux/sysfs.h:773 [inline]
device_remove_file drivers/base/core.c:3061 [inline]
device_remove_file drivers/base/core.c:3057 [inline]
device_del+0x381/0x9f0 drivers/base/core.c:3866
drop_partition+0x109/0x1c0 block/partitions/core.c:273
bdev_disk_changed+0x24d/0x14f0 block/partitions/core.c:664
__loop_clr_fd+0x392/0x850 drivers/block/loop.c:1208
lo_release+0x188/0x1c0 drivers/block/loop.c:1758
blkdev_put_whole+0xad/0xf0 block/bdev.c:673
bdev_release+0x496/0x6f0 block/bdev.c:1096
blkdev_release+0x15/0x20 block/fops.c:623
__fput+0x408/0xbb0 fs/file_table.c:422
__fput_sync+0x47/0x50 fs/file_table.c:507
__do_sys_close fs/open.c:1555 [inline]
__se_sys_close fs/open.c:1540 [inline]
__x64_sys_close+0x86/0x100 fs/open.c:1540
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7feede7170a8
Code: 48 8b 05 83 9d 0d 00 64 c7 00 16 00 00 00 83 c8 ff 48 83 c4 20 5b c3 64 8b 04 25 18 00 00 00 85 c0 75 20 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 76 5b 48 8b 15 51 9d 0d 00 f7 d8 64 89 02 48 83
RSP: 002b:00007ffcb56bae78 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 00007feedeab80e0 RCX: 00007feede7170a8
RDX: 000055e713b8acf1 RSI: 00007ffcb56ba678 RDI: 0000000000000008
RBP: 000055e24da11ce0 R08: 0000000000000006 R09: 7dad85b31cc777c1
R10: 000000000000010f R11: 0000000000000246 R12: 0000000000000002
R13: 000055e24da17d80 R14: 0000000000000008 R15: 000055e24d9c72c0
</TASK>
udevd[6164]: inotify_add_watch(7, /dev/loop1p4, 10) failed: No such file or directory
I/O error, dev loop3, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Tetsuo Handa]

This dependency is added by recent bug fix commit c0a40097f0bc ("drivers:
core: synchronize really_probe() and dev_uevent()").

Commit 4a0079bc7aae ("nvdimm: Replace lockdep_mutex with local lock
classes") changed to assign nvdimm_namespace_key on dev->mutex instead of
__lockdep_no_validate__, which made lockdep to report this dependency.

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 626737a5791b Merge tag 'pinctrl-v6.10-2' of git://git.kern..
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=12b594ae980000

kernel config: https://syzkaller.appspot.com/x/.config?x=d6b9ee98d841760c
dashboard link: https://syzkaller.appspot.com/bug?extid=4762dd74e32532cda5ff
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14f21cea980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14c4963e980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-626737a5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1cffeb16f347/vmlinux-626737a5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b20910e32f0e/bzImage-626737a5.xz

mounted in repro: https://storage.googleapis.com/syzbot-assets/67438b2787f0/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4762dd...@syzkaller.appspotmail.com

Buffer I/O error on dev loop0p1, logical block 8, async page read

======================================================
WARNING: possible circular locking dependency detected
6.10.0-rc5-syzkaller-00012-g626737a5791b #0 Not tainted
------------------------------------------------------

udevd/5224 is trying to acquire lock:
ffff888029878a58 (kn->active#5){++++}-{0:0}, at: __kernfs_remove+0x281/0x670 fs/kernfs/dir.c:1486

but task is already holding lock:

ffff8880219b84c8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_open+0x41a/0xe50 block/bdev.c:897

blkdev_get_whole+0x187/0x290 block/bdev.c:700
bdev_open+0x2c7/0xe50 block/bdev.c:909
blkdev_open+0x17b/0x1f0 block/fops.c:615
do_dentry_open+0x910/0x1930 fs/open.c:955
do_open fs/namei.c:3650 [inline]
path_openat+0x1e3a/0x29f0 fs/namei.c:3807
do_filp_open+0x1dc/0x430 fs/namei.c:3834
do_sys_openat2+0x17a/0x1e0 fs/open.c:1405
do_sys_open fs/open.c:1420 [inline]
__do_sys_openat fs/open.c:1436 [inline]
__se_sys_openat fs/open.c:1431 [inline]
__x64_sys_openat+0x175/0x210 fs/open.c:1431

do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
kn->active#5 --> &nvdimm_namespace_key --> &disk->open_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&disk->open_mutex);
lock(&nvdimm_namespace_key);
lock(&disk->open_mutex);
lock(kn->active#5);

*** DEADLOCK ***

1 lock held by udevd/5224:
#0: ffff8880219b84c8 (&disk->open_mutex){+.+.}-{3:3}, at: bdev_open+0x41a/0xe50 block/bdev.c:897

stack backtrace:
CPU: 2 PID: 5224 Comm: udevd Not tainted 6.10.0-rc5-syzkaller-00012-g626737a5791b #0

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114
check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2187
check_prev_add kernel/locking/lockdep.c:3134 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain kernel/locking/lockdep.c:3869 [inline]
__lock_acquire+0x2478/0x3b30 kernel/locking/lockdep.c:5137
lock_acquire kernel/locking/lockdep.c:5754 [inline]
lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5719
kernfs_drain+0x48f/0x590 fs/kernfs/dir.c:500
__kernfs_remove+0x281/0x670 fs/kernfs/dir.c:1486
kernfs_remove_by_name_ns+0xb2/0x130 fs/kernfs/dir.c:1694
sysfs_remove_file include/linux/sysfs.h:773 [inline]
device_remove_file drivers/base/core.c:3061 [inline]
device_remove_file drivers/base/core.c:3057 [inline]
device_del+0x381/0x9f0 drivers/base/core.c:3866
drop_partition+0x109/0x1c0 block/partitions/core.c:273
bdev_disk_changed+0x24d/0x14f0 block/partitions/core.c:664

blkdev_get_whole+0x187/0x290 block/bdev.c:700
bdev_open+0x2c7/0xe50 block/bdev.c:909
blkdev_open+0x17b/0x1f0 block/fops.c:615
do_dentry_open+0x910/0x1930 fs/open.c:955
do_open fs/namei.c:3650 [inline]
path_openat+0x1e3a/0x29f0 fs/namei.c:3807
do_filp_open+0x1dc/0x430 fs/namei.c:3834
do_sys_openat2+0x17a/0x1e0 fs/open.c:1405
do_sys_open fs/open.c:1420 [inline]
__do_sys_openat fs/open.c:1436 [inline]
__se_sys_openat fs/open.c:1431 [inline]
__x64_sys_openat+0x175/0x210 fs/open.c:1431

do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7fc33c7979a4
Code: 24 20 48 8d 44 24 30 48 89 44 24 28 64 8b 04 25 18 00 00 00 85 c0 75 2c 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 76 60 48 8b 15 55 a4 0d 00 f7 d8 64 89 02 48 83
RSP: 002b:00007ffc38f9eb40 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00005569ecaa5ab0 RCX: 00007fc33c7979a4
RDX: 00000000000a0800 RSI: 00005569eca8bfb0 RDI: 00000000ffffff9c
RBP: 00005569eca8bfb0 R08: 00000000ffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000a0800
R13: 00005569ecaa7820 R14: 0000000000000001 R15: 00005569eca722c0
</TASK>
blk_print_req_error: 53 callbacks suppressed
I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory
I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory
I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory
I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
I/O error, dev loop0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
I/O error, dev loop0, sector 108 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
Buffer I/O error on dev loop0p1, logical block 8, async page read
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory
blk_print_req_error: 138 callbacks suppressed
I/O error, dev loop0, sector 108 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory
udevd[5224]: inotify_add_watch(7, /dev/loop0p1, 10) failed: No such file or directory


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

[Dan Williams]

Tetsuo Handa wrote:
> This dependency is added by recent bug fix commit c0a40097f0bc ("drivers:
> core: synchronize really_probe() and dev_uevent()").
>
> Commit 4a0079bc7aae ("nvdimm: Replace lockdep_mutex with local lock
> classes") changed to assign nvdimm_namespace_key on dev->mutex instead of
> __lockdep_no_validate__, which made lockdep to report this dependency.

At first glance this looks like a true positive lockdep report. One
observation is that attributes that depend on dev->driver being stable
are typically more appropriate as a driver lifetime scoped attribute
rather than adding locking within the attribute handler.

So a rough idea for an alternate fix would be something like:

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 83d352394fdf..a0536e6eaea3 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -672,6 +672,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
goto probe_failed;
}

+ device_remove_file(dev, &dev_attr_uevent);
+ device_create_file(dev, &dev_attr_driver_uevent);
ret = device_add_groups(dev, drv->dev_groups);
if (ret) {
dev_err(dev, "device_add_groups() failed\n");

...where the only difference between those 2 attributes is that
dev_attr_driver_uevent additionally appends the "DRIVER=" key to the
uevent.

The problem with the above though is userspace may not expect that it
needs to re-open the uevent file over a driver attach / detach event.

Either way I think c0a40097f0bc ("drivers: core: synchronize
really_probe() and dev_uevent()") is potentially more of a band-aid than
a fix.