KCSAN: data-race in __ext4_new_inode / find_next_zero_bit (3)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 245a4300 Merge branch 'rcu/kcsan' into tip/locking/kcsan
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=176c6f51e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a38292766f8efdaa
dashboard link: https://syzkaller.appspot.com/bug?extid=f18262d081e0ff825670
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+f18262...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __ext4_new_inode / find_next_zero_bit

write to 0xffff8881237d3070 of 8 bytes by task 26216 on cpu 1:
__test_and_set_bit include/asm-generic/bitops/instrumented-non-atomic.h:76
[inline]
__test_and_set_bit_le include/asm-generic/bitops/le.h:90 [inline]
__ext4_new_inode+0xf39/0x2f10 fs/ext4/ialloc.c:939
ext4_symlink+0x31c/0x9b0 fs/ext4/namei.c:3275
vfs_symlink fs/namei.c:4131 [inline]
vfs_symlink+0x218/0x310 fs/namei.c:4117
do_symlinkat+0x1a5/0x1e0 fs/namei.c:4158
__do_sys_symlink fs/namei.c:4177 [inline]
__se_sys_symlink fs/namei.c:4175 [inline]
__x64_sys_symlink+0x3f/0x50 fs/namei.c:4175
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881237d3070 of 8 bytes by task 26212 on cpu 0:
_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:710
__ext4_new_inode+0xd45/0x2f10 fs/ext4/ialloc.c:909
ext4_symlink+0x31c/0x9b0 fs/ext4/namei.c:3275
vfs_symlink fs/namei.c:4131 [inline]
vfs_symlink+0x218/0x310 fs/namei.c:4117
do_symlinkat+0x1a5/0x1e0 fs/namei.c:4158
__do_sys_symlink fs/namei.c:4177 [inline]
__se_sys_symlink fs/namei.c:4175 [inline]
__x64_sys_symlink+0x3f/0x50 fs/namei.c:4175
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: 0 PID: 26212 Comm: syz-executor.3 Not tainted 5.5.0-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.