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Date:   Sun, 31 Oct 2021 10:41:24 -0700
From:   syzbot <>
Subject: [syzbot] WARNING: ODEBUG bug in __put_task_struct


syzbot found the following issue on:

HEAD commit:    bdcc9f6a5682 Add linux-next specific files for 20211029
git tree:       linux-next
console output:
kernel config:
dashboard link:
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:

The issue was bisected to:

commit 34ced75ca1f63fac6148497971212583aa0f7a87
Author: Xiaoguang Wang <>
Date:   Mon Oct 25 05:38:48 2021 +0000

    io_uring: reduce frequent add_wait_queue() overhead for multi-shot poll request

bisection log:
final oops:
console output:

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Fixes: 34ced75ca1f6 ("io_uring: reduce frequent add_wait_queue() overhead for multi-shot poll request")

------------[ cut here ]------------
ODEBUG: free active (active state 1) object type: rcu_head hint: 0x0
WARNING: CPU: 0 PID: 6915 at lib/debugobjects.c:505 debug_print_object+0x16e/0x250 lib/debugobjects.c:505
Modules linked in:
CPU: 0 PID: 6915 Comm: kworker/0:1 Not tainted 5.15.0-rc7-next-20211029-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events io_fallback_req_func
RIP: 0010:debug_print_object+0x16e/0x250 lib/debugobjects.c:505
Code: ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 af 00 00 00 48 8b 14 dd 00 4f bf 89 4c 89 ee 48 c7 c7 00 43 bf 89 e8 88 45 2e 05 <0f> 0b 83 05 05 c1 9f 09 01 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e c3
RSP: 0018:ffffc900033a7a98 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000000000
RDX: ffff88801a799d40 RSI: ffffffff815f3788 RDI: fffff52000674f45
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815ed55e R11: 0000000000000000 R12: ffffffff896d62a0
R13: ffffffff89bf4940 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff9fb60898 CR3: 000000000b48e000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __debug_check_no_obj_freed lib/debugobjects.c:992 [inline]
 debug_check_no_obj_freed+0x301/0x420 lib/debugobjects.c:1023
 slab_free_hook mm/slub.c:1698 [inline]
 slab_free_freelist_hook+0xeb/0x1c0 mm/slub.c:1749
 slab_free mm/slub.c:3513 [inline]
 kmem_cache_free+0x92/0x5e0 mm/slub.c:3529
 __put_task_struct+0x277/0x400 kernel/fork.c:810
 put_task_struct_many include/linux/sched/task.h:120 [inline]
 io_put_task fs/io_uring.c:1773 [inline]
 __io_free_req+0x2a3/0x3c5 fs/io_uring.c:2037
 io_fallback_req_func+0xf9/0x1ae fs/io_uring.c:1335
 process_one_work+0x9b2/0x1690 kernel/workqueue.c:2298
 worker_thread+0x658/0x11f0 kernel/workqueue.c:2445
 kthread+0x405/0x4f0 kernel/kthread.c:327
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

This report is generated by a bot. It may contain errors.
See for more information about syzbot.
syzbot engineers can be reached at

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For information about bisection process see:
syzbot can test patches for this issue, for details see:

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