KCSAN: data-race in _find_next_bit.constprop.0 / ext4_free_inode

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: b12d66a6 mm, kcsan: Instrument SLAB free with ASSERT_EXCLU..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=159bd711e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=10bc0131c4924ba9
dashboard link: https://syzkaller.appspot.com/bug?extid=b43f633eb9f85e0a8ec4
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+b43f63...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in _find_next_bit.constprop.0 / ext4_free_inode

write to 0xffff8881218bc010 of 8 bytes by task 13421 on cpu 1:
instrument_write include/linux/instrumented.h:42 [inline]
__test_and_clear_bit include/asm-generic/bitops/instrumented-non-atomic.h:85 [inline]
__test_and_clear_bit_le include/asm-generic/bitops/le.h:95 [inline]
ext4_free_inode+0x5e5/0xa50 fs/ext4/ialloc.c:311
ext4_evict_inode+0x871/0xa40 fs/ext4/inode.c:315
evict+0x244/0x410 fs/inode.c:575
iput_final fs/inode.c:1571 [inline]
iput+0x371/0x4e0 fs/inode.c:1597
dentry_unlink_inode+0x281/0x2f0 fs/dcache.c:374
d_delete fs/dcache.c:2451 [inline]
d_delete+0xdb/0xe0 fs/dcache.c:2440
vfs_rmdir fs/namei.c:3966 [inline]
vfs_rmdir+0x2e2/0x300 fs/namei.c:3931
do_rmdir+0x2cb/0x300 fs/namei.c:4014
__do_sys_rmdir fs/namei.c:4032 [inline]
__se_sys_rmdir fs/namei.c:4030 [inline]
__x64_sys_rmdir+0x2f/0x40 fs/namei.c:4030
do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881218bc010 of 8 bytes by task 20127 on cpu 0:
_find_next_bit.constprop.0+0x64/0x160 lib/find_bit.c:39
find_next_zero_bit+0x38/0x50 lib/find_bit.c:87
find_next_zero_bit_le include/asm-generic/bitops/le.h:15 [inline]
find_inode_bit.isra.0+0x82/0x300 fs/ext4/ialloc.c:713
__ext4_new_inode+0xd45/0x2f30 fs/ext4/ialloc.c:912
ext4_symlink+0x31c/0x9b0 fs/ext4/namei.c:3287
vfs_symlink fs/namei.c:4201 [inline]
vfs_symlink+0x218/0x310 fs/namei.c:4187
do_symlinkat+0x1a5/0x1e0 fs/namei.c:4228
__do_sys_symlink fs/namei.c:4247 [inline]
__se_sys_symlink fs/namei.c:4245 [inline]
__x64_sys_symlink+0x3f/0x50 fs/namei.c:4245
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: 20127 Comm: syz-executor.2 Not tainted 5.6.0-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.