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BUG: KCSAN: data-race in __blkdev_get / __blkdev_put

write to 0xffff888101393720 of 4 bytes by task 27741 on cpu 1:
 __blkdev_get+0xc1/0x6d0 fs/block_dev.c:1363
 blkdev_get_by_dev+0x9b/0x480 fs/block_dev.c:1451
 blkdev_get_by_path+0x110/0x1b0 fs/block_dev.c:1515
 mount_bdev+0x47/0x290 fs/super.c:1326
 ext4_mount+0x2d/0x40 fs/ext4/super.c:6632
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4a/0x1a0 fs/super.c:1498
 do_new_mount fs/namespace.c:2905 [inline]
 path_mount+0x11d4/0x1ce0 fs/namespace.c:3235
 do_mount fs/namespace.c:3248 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3433
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3433
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888101393720 of 4 bytes by task 1032 on cpu 0:
 __blkdev_put+0x5a/0x460 fs/block_dev.c:1566
 blkdev_put+0x23e/0x2c0 fs/block_dev.c:1636
 blkdev_close+0x47/0x50 fs/block_dev.c:1644
 __fput+0x25b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0xae/0x130 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:208
 __syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
 do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1032 Comm: systemd-udevd Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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