KCSAN: data-race in vfs_readlink / vfs_readlink (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 31f02006 Merge tag 'char-misc-5.10-rc2' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1750fd14500000
kernel config: https://syzkaller.appspot.com/x/.config?x=1dbf0ab7718f3df5
dashboard link: https://syzkaller.appspot.com/bug?extid=1b4f8047c268f8c57bb9
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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+1b4f80...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in vfs_readlink / vfs_readlink

read-write to 0xffff88800bde8a42 of 2 bytes by task 12623 on cpu 1:
vfs_readlink+0x203/0x250 fs/namei.c:4546
do_readlinkat+0x170/0x200 fs/stat.c:419
__do_sys_readlinkat fs/stat.c:434 [inline]
__se_sys_readlinkat fs/stat.c:431 [inline]
__x64_sys_readlinkat+0x4f/0x60 fs/stat.c:431
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88800bde8a42 of 2 bytes by task 12615 on cpu 0:
vfs_readlink+0x56/0x250 fs/namei.c:4538
do_readlinkat+0x170/0x200 fs/stat.c:419
__do_sys_readlinkat fs/stat.c:434 [inline]
__se_sys_readlinkat fs/stat.c:431 [inline]
__x64_sys_readlinkat+0x4f/0x60 fs/stat.c:431
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 12615 Comm: systemd-udevd Not tainted 5.10.0-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: 0 PID: 12615 Comm: systemd-udevd Not tainted 5.10.0-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+0x116/0x15d lib/dump_stack.c:118
panic+0x1e7/0x5fa kernel/panic.c:231
kcsan_report+0x67b/0x680 kernel/kcsan/report.c:634
kcsan_setup_watchpoint+0x46a/0x4d0 kernel/kcsan/core.c:568
vfs_readlink+0x56/0x250 fs/namei.c:4538
do_readlinkat+0x170/0x200 fs/stat.c:419
__do_sys_readlinkat fs/stat.c:434 [inline]
__se_sys_readlinkat fs/stat.c:431 [inline]
__x64_sys_readlinkat+0x4f/0x60 fs/stat.c:431
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f685abdb0ba
Code: 48 8b 0d e1 bd 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 49 89 ca b8 0b 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d ae bd 2b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffe51b07248 EFLAGS: 00000206 ORIG_RAX: 000000000000010b
RAX: ffffffffffffffda RBX: 0000557650d6b650 RCX: 00007f685abdb0ba
RDX: 0000557650d6b650 RSI: 00007ffe51b072d0 RDI: 00000000ffffff9c
RBP: 0000000000000064 R08: 000000000000c081 R09: 0000000000000070
R10: 0000000000000063 R11: 0000000000000206 R12: 00007ffe51b072d0
R13: 00000000ffffff9c R14: 00007ffe51b072a0 R15: 0000000000000063
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This report 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 issue. 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.