KCSAN: data-race in generic_fillattr / shmem_mknod

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 766d004d 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=11345931e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=cd9253e6e662bbb3
dashboard link: https://syzkaller.appspot.com/bug?extid=7f802edaeaa4b516acfe
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+7f802e...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in generic_fillattr / shmem_mknod

read to 0xffff888126177728 of 16 bytes by task 13895 on cpu 0:
generic_fillattr+0x16a/0x1e0 fs/stat.c:47
vfs_getattr_nosec+0x160/0x170 fs/stat.c:86
vfs_getattr+0x54/0x70 fs/stat.c:120
vfs_statx+0x108/0x190 fs/stat.c:201
vfs_stat include/linux/fs.h:3271 [inline]
__do_sys_newstat+0x51/0xb0 fs/stat.c:351
__se_sys_newstat fs/stat.c:347 [inline]
__x64_sys_newstat+0x3a/0x50 fs/stat.c:347
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff888126177728 of 16 bytes by task 13897 on cpu 1:
shmem_mknod+0x12f/0x180 mm/shmem.c:2898
shmem_create+0x34/0x50 mm/shmem.c:2945
lookup_open fs/namei.c:3309 [inline]
do_last fs/namei.c:3401 [inline]
path_openat+0x29cd/0x3150 fs/namei.c:3607
do_filp_open+0x11e/0x1b0 fs/namei.c:3637
do_sys_openat2+0x4f5/0x620 fs/open.c:1149
do_sys_open+0xa3/0x110 fs/open.c:1165
ksys_open include/linux/syscalls.h:1386 [inline]
__do_sys_open fs/open.c:1171 [inline]
__se_sys_open fs/open.c:1169 [inline]
__x64_sys_open+0x55/0x70 fs/open.c:1169
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: 1 PID: 13897 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.