[syzbot] KCSAN: data-race in call_rcu / rcu_gp_kthread

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    e73f0f0e Linux 5.14-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=172196d2300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f5e73542d774430b
dashboard link: https://syzkaller.appspot.com/bug?extid=e08a83a1940ec3846cd5
compiler:       Debian clang version 11.0.1-2

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+e08a83a1940ec3846cd5@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KCSAN: data-race in call_rcu / rcu_gp_kthread

write to 0xffffffff837328a0 of 8 bytes by task 11 on cpu 0:
 rcu_gp_fqs kernel/rcu/tree.c:1949 [inline]
 rcu_gp_fqs_loop kernel/rcu/tree.c:2010 [inline]
 rcu_gp_kthread+0xd78/0xec0 kernel/rcu/tree.c:2169
 kthread+0x262/0x280 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

read to 0xffffffff837328a0 of 8 bytes by task 30193 on cpu 1:
 __call_rcu_core kernel/rcu/tree.c:2946 [inline]
 __call_rcu kernel/rcu/tree.c:3062 [inline]
 call_rcu+0x4b0/0x6c0 kernel/rcu/tree.c:3109
 file_free fs/file_table.c:58 [inline]
 __fput+0x43e/0x4e0 fs/file_table.c:298
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:164
 get_signal+0x156c/0x15e0 kernel/signal.c:2581
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:865
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x49/0x90 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000f57 -> 0x0000000000000f58

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 30193 Comm: syz-executor.5 Tainted: G        W         5.14.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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