KCSAN: data-race in do_readlinkat / vfs_unlink (2)

[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=16d0d720100000
kernel config: https://syzkaller.appspot.com/x/.config?x=312e39c74fd784a1
dashboard link: https://syzkaller.appspot.com/bug?extid=81be6c24a4710807d848
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+81be6c...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in do_readlinkat / vfs_unlink

write to 0xffff88811cd10cc0 of 4 bytes by task 11588 on cpu 0:
dont_mount include/linux/dcache.h:352 [inline]
vfs_unlink+0x267/0x400 fs/namei.c:3811
do_unlinkat+0x33f/0x550 fs/namei.c:3873
__do_sys_unlink fs/namei.c:3920 [inline]
__se_sys_unlink fs/namei.c:3918 [inline]
__x64_sys_unlink+0x38/0x50 fs/namei.c:3918
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88811cd10cc0 of 4 bytes by task 3957 on cpu 1:
d_is_symlink include/linux/dcache.h:419 [inline]
do_readlinkat+0xe3/0x230 fs/stat.c:417
__do_sys_readlink fs/stat.c:442 [inline]
__se_sys_readlink fs/stat.c:439 [inline]
__x64_sys_readlink+0x4c/0x60 fs/stat.c:439
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: 1 PID: 3957 Comm: systemd-udevd Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 3957 Comm: systemd-udevd Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x11d/0x187 lib/dump_stack.c:118
panic+0x210/0x640 kernel/panic.c:221
kcsan_report.cold+0xc/0x1a kernel/kcsan/report.c:626
kcsan_setup_watchpoint+0x3fb/0x440 kernel/kcsan/core.c:519
d_is_symlink include/linux/dcache.h:419 [inline]
do_readlinkat+0xe3/0x230 fs/stat.c:417
__do_sys_readlink fs/stat.c:442 [inline]
__se_sys_readlink fs/stat.c:439 [inline]
__x64_sys_readlink+0x4c/0x60 fs/stat.c:439
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fbf7b4a1087
Code: 73 01 c3 48 8b 0d 11 be 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 59 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d e1 bd 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffe9c46ea98 EFLAGS: 00000293 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffe9c46eb30 RCX: 00007fbf7b4a1087
RDX: 0000000000000200 RSI: 00007ffe9c46ec40 RDI: 00007ffe9c46eb10
RBP: 00007ffe9c46f098 R08: 0000000000000001 R09: 0000000000000013
R10: 0000000000000064 R11: 0000000000000293 R12: 00007ffe9c46ec40
R13: 000055e814046010 R14: 000055e8140460e0 R15: 00007ffe9c46eb10
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

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