[syzbot] [autofs?] possible deadlock in pipe_write (2)

From: syzbot
Date: Wed Feb 05 2025 - 17:22:32 EST

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Hello,

syzbot found the following issue on:

HEAD commit: 69e858e0b8b2 Merge tag 'uml-for-linus-6.14-rc1' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15d2fddf980000
kernel config: https://syzkaller.appspot.com/x/.config?x=57ab43c279fa614d
dashboard link: https://syzkaller.appspot.com/bug?extid=25dd3743576b83be4773
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7b9951b25c33/disk-69e858e0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3814bbc0e86f/vmlinux-69e858e0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/da44e7be7454/bzImage-69e858e0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+25dd3743576b83be4773@xxxxxxxxxxxxxxxxxxxxxxxxx

======================================================
WARNING: possible circular locking dependency detected
6.13.0-syzkaller-09760-g69e858e0b8b2 #0 Not tainted
------------------------------------------------------
syz.1.2997/15256 is trying to acquire lock:
ffff888011f30468 (&pipe->mutex){+.+.}-{4:4}, at: pipe_write+0x1c6/0x1a30 fs/pipe.c:456

but task is already holding lock:
ffff888022e95140 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff888022e95140 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x71a/0xf70 fs/autofs/waitq.c:164

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&sbi->pipe_mutex){+.+.}-{4:4}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x71a/0xf70 fs/autofs/waitq.c:164
autofs_wait+0x10b8/0x1b30 fs/autofs/waitq.c:426
autofs_mount_wait+0x170/0x330 fs/autofs/root.c:255
autofs_d_automount+0x555/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1454 [inline]
__traverse_mounts+0x2ba/0x580 fs/namei.c:1499
traverse_mounts fs/namei.c:1528 [inline]
handle_mounts fs/namei.c:1631 [inline]
step_into+0x5e5/0x10b0 fs/namei.c:1952
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2636
filename_lookup+0x2a3/0x670 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xc5/0x290 block/bdev.c:1163
resume_store+0x1a0/0x710 kernel/power/hibernate.c:1247
kernfs_fop_write_iter+0x3a0/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0xacf/0xd10 fs/read_write.c:679
ksys_write+0x18f/0x2b0 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&of->mutex){+.+.}-{4:4}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
kernfs_fop_write_iter+0x1ea/0x500 fs/kernfs/file.c:325
iter_file_splice_write+0xbfa/0x1510 fs/splice.c:743
do_splice_from fs/splice.c:941 [inline]
do_splice+0xd68/0x18b0 fs/splice.c:1354
__do_splice fs/splice.c:1436 [inline]
__do_sys_splice fs/splice.c:1639 [inline]
__se_sys_splice+0x2e0/0x450 fs/splice.c:1621
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&pipe->mutex){+.+.}-{4:4}:
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
__lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
pipe_write+0x1c6/0x1a30 fs/pipe.c:456
__kernel_write_iter+0x4b3/0x950 fs/read_write.c:612
__kernel_write+0x120/0x180 fs/read_write.c:632
autofs_write fs/autofs/waitq.c:57 [inline]
autofs_notify_daemon+0x72d/0xf70 fs/autofs/waitq.c:164
autofs_wait+0x10b8/0x1b30 fs/autofs/waitq.c:426
autofs_mount_wait+0x170/0x330 fs/autofs/root.c:255
autofs_d_automount+0x555/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1454 [inline]
__traverse_mounts+0x2ba/0x580 fs/namei.c:1499
traverse_mounts fs/namei.c:1528 [inline]
handle_mounts fs/namei.c:1631 [inline]
step_into+0x5e5/0x10b0 fs/namei.c:1952
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2636
filename_lookup+0x2a3/0x670 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xc5/0x290 block/bdev.c:1163
resume_store+0x1a0/0x710 kernel/power/hibernate.c:1247
kernfs_fop_write_iter+0x3a0/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0xacf/0xd10 fs/read_write.c:679
ksys_write+0x18f/0x2b0 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
&pipe->mutex --> &of->mutex --> &sbi->pipe_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&sbi->pipe_mutex);
lock(&of->mutex);
lock(&sbi->pipe_mutex);
lock(&pipe->mutex);

*** DEADLOCK ***

5 locks held by syz.1.2997/15256:
#0: ffff888030adcd38 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x254/0x320 fs/file.c:1192
#1: ffff8880359fa420 (sb_writers#8){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:3023 [inline]
#1: ffff8880359fa420 (sb_writers#8){.+.+}-{0:0}, at: vfs_write+0x225/0xd10 fs/read_write.c:675
#2: ffff88804665a888 (&of->mutex){+.+.}-{4:4}, at: kernfs_fop_write_iter+0x1ea/0x500 fs/kernfs/file.c:325
#3: ffff8881412ffa58 (kn->active#59){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x20e/0x500 fs/kernfs/file.c:326
#4: ffff888022e95140 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_write fs/autofs/waitq.c:55 [inline]
#4: ffff888022e95140 (&sbi->pipe_mutex){+.+.}-{4:4}, at: autofs_notify_daemon+0x71a/0xf70 fs/autofs/waitq.c:164

stack backtrace:
CPU: 1 UID: 0 PID: 15256 Comm: syz.1.2997 Not tainted 6.13.0-syzkaller-09760-g69e858e0b8b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2076
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2208
check_prev_add kernel/locking/lockdep.c:3163 [inline]
check_prevs_add kernel/locking/lockdep.c:3282 [inline]
validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
__lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__mutex_lock_common kernel/locking/mutex.c:585 [inline]
__mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
pipe_write+0x1c6/0x1a30 fs/pipe.c:456
__kernel_write_iter+0x4b3/0x950 fs/read_write.c:612
__kernel_write+0x120/0x180 fs/read_write.c:632
autofs_write fs/autofs/waitq.c:57 [inline]
autofs_notify_daemon+0x72d/0xf70 fs/autofs/waitq.c:164
autofs_wait+0x10b8/0x1b30 fs/autofs/waitq.c:426
autofs_mount_wait+0x170/0x330 fs/autofs/root.c:255
autofs_d_automount+0x555/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1454 [inline]
__traverse_mounts+0x2ba/0x580 fs/namei.c:1499
traverse_mounts fs/namei.c:1528 [inline]
handle_mounts fs/namei.c:1631 [inline]
step_into+0x5e5/0x10b0 fs/namei.c:1952
lookup_last fs/namei.c:2612 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2636
filename_lookup+0x2a3/0x670 fs/namei.c:2665
kern_path+0x35/0x50 fs/namei.c:2773
lookup_bdev+0xc5/0x290 block/bdev.c:1163
resume_store+0x1a0/0x710 kernel/power/hibernate.c:1247
kernfs_fop_write_iter+0x3a0/0x500 fs/kernfs/file.c:334
new_sync_write fs/read_write.c:586 [inline]
vfs_write+0xacf/0xd10 fs/read_write.c:679
ksys_write+0x18f/0x2b0 fs/read_write.c:731
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f504898cda9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f50498d2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f5048ba5fa0 RCX: 00007f504898cda9
RDX: 0000000000000012 RSI: 0000000020000000 RDI: 0000000000000008
RBP: 00007f5048a0e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f5048ba5fa0 R15: 00007ffe28e15a78
</TASK>
PM: Image not found (code -6)

---
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Next message: Pavel Begunkov: "Re: [PATCH RFC net-next v1 5/5] net: devmem: Implement TX path"
Previous message: Dan Williams: "Re: [PATCH v6 4/6] acpi/ghes, cper: Recognize and cache CXL Protocol errors"
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