syzbot


possible deadlock in __io_queue_deferred

Status: fixed on 2020/09/16 22:51
Subsystems: fs io-uring
[Documentation on labels]
Reported-by: syzbot+996f91b6ec3812c48042@syzkaller.appspotmail.com
Fix commit: 7271ef3a93a8 io_uring: fix recursive completion locking on oveflow flush
First crash: 1435d, last: 1435d
Cause bisection: failed (error log, bisect log)
  
Duplicate bugs (1)
duplicates (1):
Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
possible deadlock in io_queue_linked_timeout io-uring fs C error 3 1431d 1434d 0/27 closed as dup on 2020/08/10 16:02
Discussions (2)
Title Replies (including bot) Last reply
possible deadlock in __io_queue_deferred 5 (6) 2020/08/11 14:45
possible deadlock in io_queue_linked_timeout 1 (2) 2020/08/10 15:59

Sample crash report:
============================================
WARNING: possible recursive locking detected
5.8.0-syzkaller #0 Not tainted
--------------------------------------------
syz-executor287/6816 is trying to acquire lock:
ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: spin_lock_irq include/linux/spinlock.h:379 [inline]
ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: io_queue_linked_timeout fs/io_uring.c:5928 [inline]
ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: __io_queue_async_work fs/io_uring.c:1192 [inline]
ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: __io_queue_deferred+0x36a/0x790 fs/io_uring.c:1237

but task is already holding lock:
ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: io_cqring_overflow_flush+0xc6/0xab0 fs/io_uring.c:1333

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

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

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor287/6816:
 #0: ffff888093cdb4d8 (&ctx->completion_lock){....}-{2:2}, at: io_cqring_overflow_flush+0xc6/0xab0 fs/io_uring.c:1333

stack backtrace:
CPU: 1 PID: 6816 Comm: syz-executor287 Not tainted 5.8.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1f0/0x31e lib/dump_stack.c:118
 print_deadlock_bug kernel/locking/lockdep.c:2391 [inline]
 check_deadlock kernel/locking/lockdep.c:2432 [inline]
 validate_chain+0x69a4/0x88a0 kernel/locking/lockdep.c:3202
 __lock_acquire+0x1161/0x2ab0 kernel/locking/lockdep.c:4426
 lock_acquire+0x160/0x730 kernel/locking/lockdep.c:5005
 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
 _raw_spin_lock_irq+0x67/0x80 kernel/locking/spinlock.c:167
 spin_lock_irq include/linux/spinlock.h:379 [inline]
 io_queue_linked_timeout fs/io_uring.c:5928 [inline]
 __io_queue_async_work fs/io_uring.c:1192 [inline]
 __io_queue_deferred+0x36a/0x790 fs/io_uring.c:1237
 io_cqring_overflow_flush+0x774/0xab0 fs/io_uring.c:1359
 io_ring_ctx_wait_and_kill+0x2a1/0x570 fs/io_uring.c:7808
 io_uring_release+0x59/0x70 fs/io_uring.c:7829
 __fput+0x34f/0x7b0 fs/file_table.c:281
 task_work_run+0x137/0x1c0 kernel/task_work.c:135
 exit_task_work include/linux/task_work.h:25 [inline]
 do_exit+0x5f3/0x1f20 kernel/exit.c:806
 do_group_exit+0x161/0x2d0 kernel/exit.c:903
 __do_sys_exit_group+0x13/0x20 kernel/exit.c:914
 __se_sys_exit_group+0x10/0x10 kernel/exit.c:912
 __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
 do_syscall_64+0x31/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x43f598
Code: Bad RIP value.
RSP: 002b:00007fffdac2bf58 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043f598
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004beda8 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d11a0 R14: 0000000000000000 R15: 0000000000000000

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2020/08/09 04:39 upstream 449dc8c97089 f721e4a0 .config console log report syz C ci-upstream-kasan-gce-smack-root
* Struck through repros no longer work on HEAD.