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BUG: KCSAN: data-race in lo_ioctl / loop_queue_work

read-write to 0xffff888141fce418 of 4 bytes by task 8470 on cpu 1:
 loop_clr_fd drivers/block/loop.c:1327 [inline]
 lo_ioctl+0x4a4/0x11d0 drivers/block/loop.c:1692
 blkdev_ioctl+0x1d0/0x3c0 block/ioctl.c:576
 block_ioctl+0x6d/0x80 fs/block_dev.c:1650
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888141fce418 of 4 bytes by task 17560 on cpu 0:
 loop_handle_cmd drivers/block/loop.c:2032 [inline]
 loop_queue_work+0x8d/0x1320 drivers/block/loop.c:2055
 kthread_worker_fn+0x28f/0x530 kernel/kthread.c:710
 loop_kthread_worker_fn+0x31/0x40 drivers/block/loop.c:932
 kthread+0x1fd/0x220 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 17560 Comm: loop0 Not tainted 5.11.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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