[syzbot] WARNING: suspicious RCU usage in io_sq_thread

syzbot
2021-03-29T07:35:18Z

Hello,

syzbot found the following issue on:

HEAD commit: 81b1d39f Merge tag '5.12-rc4-smb3' of git://git.samba.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=156f3d9ed00000
kernel config: https://syzkaller.appspot.com/x/.config?x=d4e9addca54f3b44
dashboard link: https://syzkaller.appspot.com/bug?extid=0cbf22e728582ade44f2

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+0cbf22e728582ade44f2@syzkaller.appspotmail.com

WARNING: suspicious RCU usage
5.12.0-rc4-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:8294 Illegal context switch in RCU-bh read-side critical section!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 0
1 lock held by iou-sqp-10136/10139:
#0: ffff88801a5a8c70 (&sqd->lock){+.+.}-{3:3}, at: io_sq_thread+0xff2/0x13a0 fs/io_uring.c:6794

stack backtrace:
CPU: 1 PID: 10139 Comm: iou-sqp-10136 Not tainted 5.12.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
___might_sleep+0x229/0x2c0 kernel/sched/core.c:8294
io_sq_thread+0xbae/0x13a0 fs/io_uring.c:6768
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

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