KCSAN: data-race in ext4_mb_good_group / mb_mark_used

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 36756079 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=1140d58f600000
kernel config: https://syzkaller.appspot.com/x/.config?x=c0906aa620713d80
dashboard link: https://syzkaller.appspot.com/bug?extid=8e3395a2626bcc035af1
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+8e3395...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in ext4_mb_good_group / mb_mark_used

write to 0xffff88812a6e4768 of 4 bytes by task 7835 on cpu 0:
mb_mark_used+0x894/0x940 fs/ext4/mballoc.c:1586
ext4_mb_use_best_found+0x111/0x310 fs/ext4/mballoc.c:1645
ext4_mb_measure_extent fs/ext4/mballoc.c:1748 [inline]
ext4_mb_complex_scan_group+0x4ae/0x5b0 fs/ext4/mballoc.c:1978
ext4_mb_regular_allocator+0x610/0x9d0 fs/ext4/mballoc.c:2216
ext4_mb_new_blocks+0xdd3/0x1ca0 fs/ext4/mballoc.c:4539
ext4_new_meta_blocks+0x175/0x200 fs/ext4/balloc.c:657
ext4_xattr_block_set+0xec8/0x1cf0 fs/ext4/xattr.c:2068
ext4_xattr_set_handle+0x969/0xcc0 fs/ext4/xattr.c:2404
__ext4_set_acl+0x25a/0x360 fs/ext4/acl.c:214
ext4_init_acl+0x1a2/0x200 fs/ext4/acl.c:293
__ext4_new_inode+0x28f0/0x3070 fs/ext4/ialloc.c:1156
ext4_mkdir+0x289/0x820 fs/ext4/namei.c:2763
vfs_mkdir+0x283/0x390 fs/namei.c:3815
ovl_do_mkdir fs/overlayfs/overlayfs.h:125 [inline]
ovl_mkdir_real fs/overlayfs/dir.c:122 [inline]
ovl_create_real+0x1db/0x2b0 fs/overlayfs/dir.c:169

read to 0xffff88812a6e4768 of 4 bytes by task 7832 on cpu 1:
ext4_mb_good_group+0x1cd/0x410 fs/ext4/mballoc.c:2059
ext4_mb_regular_allocator+0x6e1/0x9d0 fs/ext4/mballoc.c:2183
ext4_mb_new_blocks+0xdd3/0x1ca0 fs/ext4/mballoc.c:4539
ext4_new_meta_blocks+0x175/0x200 fs/ext4/balloc.c:657
ext4_xattr_block_set+0xec8/0x1cf0 fs/ext4/xattr.c:2068
ext4_xattr_set_handle+0x969/0xcc0 fs/ext4/xattr.c:2404
__ext4_set_acl+0x25a/0x360 fs/ext4/acl.c:214
ext4_init_acl+0x1a2/0x200 fs/ext4/acl.c:293
__ext4_new_inode+0x28f0/0x3070 fs/ext4/ialloc.c:1156
ext4_mkdir+0x289/0x820 fs/ext4/namei.c:2763
vfs_mkdir+0x283/0x390 fs/namei.c:3815
ovl_do_mkdir fs/overlayfs/overlayfs.h:125 [inline]
ovl_mkdir_real fs/overlayfs/dir.c:122 [inline]
ovl_create_real+0x1db/0x2b0 fs/overlayfs/dir.c:169
ovl_workdir_create+0x299/0x3f0 fs/overlayfs/super.c:649

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7832 Comm: syz-executor.2 Not tainted 5.3.0+ #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.