KCSAN: data-race in file_update_time / generic_update_time

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c3cd68e Merge remote-tracking branch 'linux-rcu/kcsan' in..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=10abe516100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff291dc25f22cdda
dashboard link: https://syzkaller.appspot.com/bug?extid=c885d0713f0634d67191
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c885d0...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in file_update_time / generic_update_time

read to 0xffff888120ecd3d8 of 8 bytes by task 8906 on cpu 1:
file_update_time+0x12a/0x2d0 fs/inode.c:1897
pipe_write+0xbd3/0xd40 fs/pipe.c:617
call_write_iter include/linux/fs.h:1907 [inline]
new_sync_write+0x303/0x400 fs/read_write.c:484
__vfs_write+0x9e/0xb0 fs/read_write.c:497
vfs_write fs/read_write.c:559 [inline]
vfs_write+0x189/0x380 fs/read_write.c:543
ksys_write+0x16a/0x1a0 fs/read_write.c:612
__do_sys_write fs/read_write.c:624 [inline]
__se_sys_write fs/read_write.c:621 [inline]
__x64_sys_write+0x49/0x60 fs/read_write.c:621
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888120ecd3d8 of 16 bytes by task 8908 on cpu 0:
generic_update_time+0xc2/0x270 fs/inode.c:1673
update_time+0x7d/0x90 fs/inode.c:1695
file_update_time+0x205/0x2d0 fs/inode.c:1910
pipe_write+0xbd3/0xd40 fs/pipe.c:617
call_write_iter include/linux/fs.h:1907 [inline]
new_sync_write+0x303/0x400 fs/read_write.c:484
__vfs_write+0x9e/0xb0 fs/read_write.c:497
vfs_write fs/read_write.c:559 [inline]
vfs_write+0x189/0x380 fs/read_write.c:543
ksys_write+0x16a/0x1a0 fs/read_write.c:612
__do_sys_write fs/read_write.c:624 [inline]
__se_sys_write fs/read_write.c:621 [inline]
__x64_sys_write+0x49/0x60 fs/read_write.c:621
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8908 Comm: syz-fuzzer Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.