syzbot

==================================================================
BUG: KCSAN: data-race in io_sq_thread / percpu_ref_kill_and_confirm

write to 0xffff88810b411800 of 8 bytes by task 12822 on cpu 1:
 percpu_ref_kill_and_confirm+0x75/0x190 lib/percpu-refcount.c:386
 percpu_ref_kill include/linux/percpu-refcount.h:149 [inline]
 __io_uring_register fs/io_uring.c:9614 [inline]
 __do_sys_io_uring_register+0x137/0x1c50 fs/io_uring.c:9755
 __se_sys_io_uring_register fs/io_uring.c:9737 [inline]
 __x64_sys_io_uring_register+0x4f/0x60 fs/io_uring.c:9737
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810b411800 of 8 bytes by task 12813 on cpu 0:
 percpu_ref_is_dying include/linux/percpu-refcount.h:352 [inline]
 __io_sq_thread fs/io_uring.c:6701 [inline]
 io_sq_thread+0x50f/0xcd0 fs/io_uring.c:6794
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12813 Comm: io_uring-sq Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 12813 Comm: io_uring-sq Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x116/0x15d lib/dump_stack.c:120
 panic+0x1e7/0x5fa kernel/panic.c:231
 kcsan_report+0x67b/0x680 kernel/kcsan/report.c:634
 kcsan_setup_watchpoint+0x47b/0x4e0 kernel/kcsan/core.c:568
 percpu_ref_is_dying include/linux/percpu-refcount.h:352 [inline]
 __io_sq_thread fs/io_uring.c:6701 [inline]
 io_sq_thread+0x50f/0xcd0 fs/io_uring.c:6794
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
Kernel Offset: disabled
Rebooting in 86400 seconds..