KCSAN: data-race in __ext4_new_inode / find_next_zero_bit (4)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 4a21185c Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13c44955100000
kernel config: https://syzkaller.appspot.com/x/.config?x=d5bd81d2df2321b6
dashboard link: https://syzkaller.appspot.com/bug?extid=fb83855310e88185110c
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

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+fb8385...@syzkaller.appspotmail.com

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

write to 0xffff888123d593f0 of 8 bytes by task 17271 on cpu 0:
instrument_write include/linux/instrumented.h:42 [inline]
__test_and_set_bit include/asm-generic/bitops/instrumented-non-atomic.h:71 [inline]
__test_and_set_bit_le include/asm-generic/bitops/le.h:90 [inline]
__ext4_new_inode+0xeb6/0x2f60 fs/ext4/ialloc.c:957
ext4_symlink+0x351/0x7e0 fs/ext4/namei.c:3303
vfs_symlink+0x218/0x2f0 fs/namei.c:3953
do_symlinkat+0xee/0x280 fs/namei.c:3980
__do_sys_symlink fs/namei.c:3999 [inline]
__se_sys_symlink fs/namei.c:3997 [inline]
__x64_sys_symlink+0x32/0x40 fs/namei.c:3997
do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888123d593f0 of 8 bytes by task 17270 on cpu 1:
_find_next_bit lib/find_bit.c:39 [inline]
find_next_zero_bit+0x3a/0xf0 lib/find_bit.c:87
find_next_zero_bit_le include/asm-generic/bitops/le.h:15 [inline]
find_inode_bit+0x2f7/0x380 fs/ext4/ialloc.c:718
__ext4_new_inode+0xc24/0x2f60 fs/ext4/ialloc.c:927
ext4_symlink+0x351/0x7e0 fs/ext4/namei.c:3303
vfs_symlink+0x218/0x2f0 fs/namei.c:3953
do_symlinkat+0xee/0x280 fs/namei.c:3980
__do_sys_symlink fs/namei.c:3999 [inline]
__se_sys_symlink fs/namei.c:3997 [inline]
__x64_sys_symlink+0x32/0x40 fs/namei.c:3997
do_syscall_64+0x71/0x120 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 17270 Comm: syz-executor.5 Not tainted 5.8.0-rc2-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.