KCSAN: data-race in ext4_mb_find_by_goal / mb_mark_used

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c3cd68e Merge remote-tracking branch 'linux-rcu/kcsan' in..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=1161e42e100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff291dc25f22cdda
dashboard link: https://syzkaller.appspot.com/bug?extid=47daa2074a04c7113db2
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
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+47daa2...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ext4_mb_find_by_goal / mb_mark_used

write to 0xffff88821aadf2e4 of 4 bytes by task 29031 on cpu 0:
mb_mark_used+0x189/0x860 fs/ext4/mballoc.c:1574
ext4_mb_use_best_found+0x111/0x310 fs/ext4/mballoc.c:1645
ext4_mb_simple_scan_group+0x227/0x350 fs/ext4/mballoc.c:1919
ext4_mb_regular_allocator+0x7e4/0x990 fs/ext4/mballoc.c:2218
ext4_mb_new_blocks+0xe36/0x1e20 fs/ext4/mballoc.c:4568
ext4_ext_map_blocks+0x18cb/0x1fb0 fs/ext4/extents.c:4218
ext4_map_blocks+0x230/0xcf0 fs/ext4/inode.c:621
ext4_alloc_file_blocks+0x210/0x6c0 fs/ext4/extents.c:4406
ext4_fallocate+0x9dc/0x21f0 fs/ext4/extents.c:4675
vfs_fallocate+0x3b1/0x640 fs/open.c:309
ioctl_preallocate+0x12a/0x190 fs/ioctl.c:504
file_ioctl fs/ioctl.c:544 [inline]
do_vfs_ioctl+0xa69/0xd00 fs/ioctl.c:742
ksys_ioctl+0xb2/0x150 fs/ioctl.c:761
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl fs/ioctl.c:770 [inline]
__x64_sys_ioctl+0x47/0x60 fs/ioctl.c:770
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88821aadf2e4 of 4 bytes by task 29055 on cpu 1:
ext4_mb_find_by_goal+0x17e/0x7c0 fs/ext4/mballoc.c:1829
ext4_mb_regular_allocator+0xff/0x990 fs/ext4/mballoc.c:2125
ext4_mb_new_blocks+0xe36/0x1e20 fs/ext4/mballoc.c:4568
ext4_ext_map_blocks+0x18cb/0x1fb0 fs/ext4/extents.c:4218
ext4_map_blocks+0x230/0xcf0 fs/ext4/inode.c:621
ext4_alloc_file_blocks+0x210/0x6c0 fs/ext4/extents.c:4406
ext4_zero_range fs/ext4/extents.c:4554 [inline]
ext4_fallocate+0x59f/0x21f0 fs/ext4/extents.c:4643
vfs_fallocate+0x3b1/0x640 fs/open.c:309
ioctl_preallocate+0x12a/0x190 fs/ioctl.c:504
file_ioctl fs/ioctl.c:549 [inline]
do_vfs_ioctl+0xa32/0xd00 fs/ioctl.c:742
ksys_ioctl+0xb2/0x150 fs/ioctl.c:761
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl fs/ioctl.c:770 [inline]
__x64_sys_ioctl+0x47/0x60 fs/ioctl.c:770
do_syscall_64+0xc7/0x3b0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 29055 Comm: syz-executor.3 Not tainted 5.7.0-rc1-syzkaller #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.