KCSAN: data-race in __blkdev_get / __blkdev_put

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 84b13499 Merge tag 'for-linus' of git://git.kernel.org/pub..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11ab72fd900000
kernel config: https://syzkaller.appspot.com/x/.config?x=a5d60aa8b6ca55a0
dashboard link: https://syzkaller.appspot.com/bug?extid=e02873f722605affb544
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e02873...@syzkaller.appspotmail.com

loop1: p2 < >
ldm_parse_privhead(): Cannot find PRIVHEAD structure. LDM database is corrupt. Aborting.
ldm_validate_privheads(): Cannot find PRIVHEAD 1.
loop0: p2 < >
==================================================================
BUG: KCSAN: data-race in __blkdev_get / __blkdev_put

write to 0xffff8881206eba84 of 4 bytes by task 8728 on cpu 0:
__blkdev_get+0xaa9/0xe30 fs/block_dev.c:1564
blkdev_get fs/block_dev.c:1639 [inline]
blkdev_open+0x123/0x170 fs/block_dev.c:1753
do_dentry_open+0x52d/0x890 fs/open.c:817
vfs_open+0x43/0x50 fs/open.c:931
do_open fs/namei.c:3251 [inline]
path_openat+0x1844/0x20a0 fs/namei.c:3368
do_filp_open+0xbd/0x1d0 fs/namei.c:3395
do_sys_openat2+0x33b/0x500 fs/open.c:1168
do_sys_open fs/open.c:1184 [inline]
__do_sys_open fs/open.c:1192 [inline]
__se_sys_open fs/open.c:1188 [inline]
__x64_sys_open+0xe2/0x110 fs/open.c:1188
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881206eba84 of 4 bytes by task 5078 on cpu 1:
__blkdev_put+0x5c/0x4a0 fs/block_dev.c:1768
blkdev_put+0x1e6/0x210 fs/block_dev.c:1846
blkdev_close+0x47/0x50 fs/block_dev.c:1853
__fput+0x246/0x4d0 fs/file_table.c:281
____fput+0x11/0x20 fs/file_table.c:314
task_work_run+0x8e/0x110 kernel/task_work.c:141
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_user_mode_loop kernel/entry/common.c:163 [inline]
exit_to_user_mode_prepare+0x1b2/0x210 kernel/entry/common.c:190
syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:265
do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 5078 Comm: systemd-udevd Not tainted 5.9.0-rc4-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.