Re: [syzbot] possible deadlock in io_disarm_next

Pavel Begunkov <asml.silence@xxxxxxxxx> · Wed, 20 Apr 2022 13:38:22 +0100

On 4/20/22 11:00, syzbot wrote:
Hello,

syzbot found the following issue on:

HEAD commit:    634de1db0e9b Add linux-next specific files for 20220419
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10c92db8f00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bbd6f9b0a89865b0
dashboard link: https://syzkaller.appspot.com/bug?extid=57e67273f92d7f5f1931
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10a02f68f00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=138e3008f00000

The issue was bisected to:

commit 78bfbdd1a4977df1dded20f9783a6ec174e67ef8
Author: Pavel Begunkov <asml.silence@xxxxxxxxx>
Date:   Fri Apr 15 21:08:23 2022 +0000

     io_uring: kill io_put_req_deferred()

#syz test: https://github.com/isilence/linux.git syz_timeout_deadlock

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=13039c0cf00000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=10839c0cf00000
console output: https://syzkaller.appspot.com/x/log.txt?x=17039c0cf00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+57e67273f92d7f5f1931@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 78bfbdd1a497 ("io_uring: kill io_put_req_deferred()")

============================================
WARNING: possible recursive locking detected
5.18.0-rc3-next-20220419-syzkaller #0 Not tainted
--------------------------------------------
syz-executor162/3588 is trying to acquire lock:
ffff888011a453d8 (&ctx->timeout_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
ffff888011a453d8 (&ctx->timeout_lock){....}-{2:2}, at: io_disarm_next+0x545/0xaa0 fs/io_uring.c:2452

but task is already holding lock:
ffff888011a453d8 (&ctx->timeout_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
ffff888011a453d8 (&ctx->timeout_lock){....}-{2:2}, at: io_kill_timeouts+0x4c/0x227 fs/io_uring.c:10432

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-executor162/3588:
  #0: ffff888011a45398 (&ctx->completion_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:354 [inline]
  #0: ffff888011a45398 (&ctx->completion_lock){+.+.}-{2:2}, at: io_kill_timeouts+0x38/0x227 fs/io_uring.c:10431
  #1: ffff888011a453d8 (&ctx->timeout_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
  #1: ffff888011a453d8 (&ctx->timeout_lock){....}-{2:2}, at: io_kill_timeouts+0x4c/0x227 fs/io_uring.c:10432

stack backtrace:
CPU: 1 PID: 3588 Comm: syz-executor162 Not tainted 5.18.0-rc3-next-20220419-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+0xcd/0x134 lib/dump_stack.c:106
  print_deadlock_bug kernel/locking/lockdep.c:2988 [inline]
  check_deadlock kernel/locking/lockdep.c:3031 [inline]
  validate_chain kernel/locking/lockdep.c:3816 [inline]
  __lock_acquire.cold+0x1f5/0x3b4 kernel/locking/lockdep.c:5053
  lock_acquire kernel/locking/lockdep.c:5665 [inline]
  lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5630
  __raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
  _raw_spin_lock_irq+0x32/0x50 kernel/locking/spinlock.c:170
  spin_lock_irq include/linux/spinlock.h:379 [inline]
  io_disarm_next+0x545/0xaa0 fs/io_uring.c:2452
  __io_req_complete_post+0x794/0xd90 fs/io_uring.c:2200
  io_kill_timeout fs/io_uring.c:1815 [inline]
  io_kill_timeout+0x210/0x21d fs/io_uring.c:1803
  io_kill_timeouts+0xe2/0x227 fs/io_uring.c:10435
  io_ring_ctx_wait_and_kill+0x1eb/0x360 fs/io_uring.c:10462
  io_uring_release+0x42/0x46 fs/io_uring.c:10483
  __fput+0x277/0x9d0 fs/file_table.c:317
  task_work_run+0xdd/0x1a0 kernel/task_work.c:164
  exit_task_work include/linux/task_work.h:37 [inline]
  do_exit+0xaff/0x2a00 kernel/exit.c:796
  do_group_exit+0xd2/0x2f0 kernel/exit.c:926
  __do_sys_exit_group kernel/exit.c:937 [inline]
  __se_sys_exit_group kernel/exit.c:935 [inline]
  __x64_sys_exit_group+0x3a/0x50 kernel/exit.c:935
  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
  entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f786cb8ccb9
Code: Unable to access opcode bytes at RIP 0x7f786cb8cc8f.
RSP: 002b:00007ffcf6b5b088 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f786cc01350 RCX: 00007f786cb8ccb9
RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffffffffffc0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f786cc01350
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
  </TASK>

---
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--
Pavel Begunkov