linux-kernel - [syzbot] possible deadlock in io_flush

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Date:   Fri, 26 Nov 2021 03:49:21 -0800
From:   syzbot <syzbot+847f02ec20a6609a328b@...kaller.appspotmail.com>
To:     asml.silence@...il.com, axboe@...nel.dk, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: [syzbot] possible deadlock in io_flush_timeouts

Hello,

syzbot found the following issue on:

HEAD commit:    a4849f6000e2 Merge tag 'drm-fixes-2021-11-26' of git://ano..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=155d6431b00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=178bb64dabf569c5
dashboard link: https://syzkaller.appspot.com/bug?extid=847f02ec20a6609a328b
compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.2

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+847f02ec20a6609a328b@...kaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
5.16.0-rc2-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.5/3756 is trying to acquire lock:
ffff88807c93b418 (&ctx->timeout_lock){+.+.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:374 [inline]
ffff88807c93b418 (&ctx->timeout_lock){+.+.}-{2:2}, at: io_flush_timeouts+0x80/0x34c fs/io_uring.c:1587

but task is already holding lock:
ffff88807c93b418 (&ctx->timeout_lock){+.+.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:374 [inline]
ffff88807c93b418 (&ctx->timeout_lock){+.+.}-{2:2}, at: io_poll_remove_all+0x49/0x319 fs/io_uring.c:5702

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&ctx->timeout_lock);
  lock(&ctx->timeout_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor.5/3756:
 #0: ffff88807c93b3d8 (&ctx->completion_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
 #0: ffff88807c93b3d8 (&ctx->completion_lock){+.+.}-{2:2}, at: io_poll_remove_all+0x38/0x319 fs/io_uring.c:5701
 #1: ffff88807c93b418 (&ctx->timeout_lock){+.+.}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:374 [inline]
 #1: ffff88807c93b418 (&ctx->timeout_lock){+.+.}-{2:2}, at: io_poll_remove_all+0x49/0x319 fs/io_uring.c:5702

stack backtrace:
CPU: 1 PID: 3756 Comm: syz-executor.5 Not tainted 5.16.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1dc/0x2d8 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2956 [inline]
 check_deadlock kernel/locking/lockdep.c:2999 [inline]
 validate_chain+0x5984/0x8240 kernel/locking/lockdep.c:3788
 __lock_acquire+0x1382/0x2b00 kernel/locking/lockdep.c:5027
 lock_acquire+0x19f/0x4d0 kernel/locking/lockdep.c:5637
 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
 _raw_spin_lock_irq+0xcf/0x110 kernel/locking/spinlock.c:170
 spin_lock_irq include/linux/spinlock.h:374 [inline]
 io_flush_timeouts+0x80/0x34c fs/io_uring.c:1587
 __io_commit_cqring_flush+0x80/0xbf fs/io_uring.c:1618
 io_commit_cqring fs/io_uring.c:1626 [inline]
 io_poll_remove_one+0x4bd/0x610 fs/io_uring.c:5684
 io_poll_remove_all+0x24c/0x319 fs/io_uring.c:5709
 io_ring_ctx_wait_and_kill+0x22c/0x36a fs/io_uring.c:9534
 io_uring_release+0x59/0x63 fs/io_uring.c:9554
 __fput+0x3fc/0x870 fs/file_table.c:280
 task_work_run+0x146/0x1c0 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x209/0x220 kernel/entry/common.c:207
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x2e/0x70 kernel/entry/common.c:300
 do_syscall_64+0x53/0xd0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f8fcca06ae9
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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8fc9f7c188 EFLAGS: 00000246 ORIG_RAX: 0000000000000124
RAX: 0000000000000004 RBX: 00007f8fccb19f60 RCX: 00007f8fcca06ae9
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00007f8fcca60f6d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffdd4f85a4f R14: 00007f8fc9f7c300 R15: 0000000000022000
 </TASK>


---
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