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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 805c6d3c Merge branch 'fixes' of git://git.kernel.org/pub/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14ef904b900000
kernel config: https://syzkaller.appspot.com/x/.config?x=7b00edac59eadd4a
dashboard link: https://syzkaller.appspot.com/bug?extid=d64a7b91f17b590f54c3
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
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+d64a7b...@syzkaller.appspotmail.com

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

write to 0xffff8880a8edad80 of 4 bytes by task 19245 on cpu 1:
dont_mount include/linux/dcache.h:354 [inline]
vfs_unlink+0x271/0x3c0 fs/namei.c:3834
do_unlinkat+0x28a/0x4d0 fs/namei.c:3896
__do_sys_unlink fs/namei.c:3942 [inline]
__se_sys_unlink fs/namei.c:3940 [inline]
__x64_sys_unlink+0x2c/0x30 fs/namei.c:3940
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880a8edad80 of 4 bytes by task 5080 on cpu 0:
__d_entry_type include/linux/dcache.h:391 [inline]
d_is_symlink include/linux/dcache.h:421 [inline]
vfs_readlink+0x1c1/0x260 fs/namei.c:4541
do_readlinkat+0x170/0x200 fs/stat.c:431
__do_sys_readlink fs/stat.c:452 [inline]
__se_sys_readlink fs/stat.c:449 [inline]
__x64_sys_readlink+0x43/0x50 fs/stat.c:449
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: 5080 Comm: systemd-udevd Not tainted 5.9.0-rc6-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: 5080 Comm: systemd-udevd Not tainted 5.9.0-rc6-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+0x10f/0x19d lib/dump_stack.c:118
panic+0x207/0x64a kernel/panic.c:231
kcsan_report+0x684/0x690 kernel/kcsan/report.c:630
kcsan_setup_watchpoint+0x41e/0x4a0 kernel/kcsan/core.c:540
__d_entry_type include/linux/dcache.h:391 [inline]
d_is_symlink include/linux/dcache.h:421 [inline]
vfs_readlink+0x1c1/0x260 fs/namei.c:4541
do_readlinkat+0x170/0x200 fs/stat.c:431
__do_sys_readlink fs/stat.c:452 [inline]
__se_sys_readlink fs/stat.c:449 [inline]
__x64_sys_readlink+0x43/0x50 fs/stat.c:449
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7fcb58875087
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:00007ffc6ff074e8 EFLAGS: 00000293 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffc6ff07580 RCX: 00007fcb58875087
RDX: 0000000000000200 RSI: 00007ffc6ff07690 RDI: 00007ffc6ff07560
RBP: 00007ffc6ff07ae8 R08: 0000000000000001 R09: 0000000000000013
R10: 0000000000000064 R11: 0000000000000293 R12: 00007ffc6ff07690
R13: 000055bbda36c010 R14: 000055bbda36c0e0 R15: 00007ffc6ff07560
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

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