KCSAN: data-race in atime_needs_update / shmem_unlink

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b12d66a6 mm, kcsan: Instrument SLAB free with ASSERT_EXCLU..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=115a5c09e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=10bc0131c4924ba9
dashboard link: https://syzkaller.appspot.com/bug?extid=cbb38bc529febfc7d5fa
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk el...@google.com]

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+cbb38b...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in atime_needs_update / shmem_unlink

read to 0xffff888051358f10 of 8 bytes by task 4030 on cpu 1:
relatime_need_update fs/inode.c:1647 [inline]
atime_needs_update+0x264/0x360 fs/inode.c:1732
touch_atime+0x63/0x150 fs/inode.c:1747
do_readlinkat+0x1d8/0x220 fs/stat.c:420
__do_sys_readlink fs/stat.c:442 [inline]
__se_sys_readlink fs/stat.c:439 [inline]
__x64_sys_readlink+0x51/0x70 fs/stat.c:439
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888051358f10 of 16 bytes by task 16957 on cpu 0:
shmem_unlink+0xe8/0x150 mm/shmem.c:2987
vfs_unlink+0x225/0x3e0 fs/namei.c:4073
do_unlinkat+0x32b/0x530 fs/namei.c:4137
__do_sys_unlink fs/namei.c:4184 [inline]
__se_sys_unlink fs/namei.c:4182 [inline]
__x64_sys_unlink+0x3b/0x50 fs/namei.c:4182
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16957 Comm: udevd Not tainted 5.6.0-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.