KCSAN: data-race in ext4_free_inode / find_next_zero_bit (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 05f22368 x86, kcsan: Enable KCSAN for x86
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=17427ac0e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
dashboard link: https://syzkaller.appspot.com/bug?extid=c092409cdb3bc5261b1f
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [adilger...@dilger.ca linux...@vger.kernel.org
linux-...@vger.kernel.org ty...@mit.edu 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+c09240...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ext4_free_inode / find_next_zero_bit

write to 0xffff88812310d028 of 8 bytes by task 7275 on cpu 0:
__test_and_clear_bit include/asm-generic/bitops-instrumented.h:213 [inline]
__test_and_clear_bit_le include/asm-generic/bitops/le.h:95 [inline]
ext4_free_inode+0x5f1/0xaa0 fs/ext4/ialloc.c:313
ext4_evict_inode+0x9a9/0xdb0 fs/ext4/inode.c:333
evict+0x244/0x410 fs/inode.c:574
iput_final fs/inode.c:1563 [inline]
iput+0x371/0x4e0 fs/inode.c:1589
do_unlinkat+0x378/0x530 fs/namei.c:4061
__do_sys_unlink fs/namei.c:4102 [inline]
__se_sys_unlink fs/namei.c:4100 [inline]
__x64_sys_unlink+0x3b/0x50 fs/namei.c:4100
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812310d028 of 8 bytes by task 9703 on cpu 1:
_find_next_bit lib/find_bit.c:39 [inline]
find_next_zero_bit+0x4e/0xe0 lib/find_bit.c:79
find_next_zero_bit_le include/asm-generic/bitops/le.h:15 [inline]
find_inode_bit.isra.0+0x82/0x300 fs/ext4/ialloc.c:715
__ext4_new_inode+0xd4b/0x3070 fs/ext4/ialloc.c:914
ext4_symlink+0x30e/0x970 fs/ext4/namei.c:3262
vfs_symlink fs/namei.c:4119 [inline]
vfs_symlink+0x218/0x310 fs/namei.c:4105
do_symlinkat+0x1a5/0x1e0 fs/namei.c:4146
__do_sys_symlink fs/namei.c:4165 [inline]
__se_sys_symlink fs/namei.c:4163 [inline]
__x64_sys_symlink+0x3f/0x50 fs/namei.c:4163
do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9703 Comm: syz-executor.2 Not tainted 5.4.0-rc3+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
==================================================================


---
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.