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BUG: KCSAN: data-race in __loop_clr_fd / blkdev_common_ioctl

write to 0xffff8881299253f0 of 4 bytes by task 22117 on cpu 0:
 __loop_clr_fd+0x52e/0x5b0 drivers/block/loop.c:1301
 loop_clr_fd drivers/block/loop.c:1345 [inline]
 lo_ioctl+0x9d1/0x1190 drivers/block/loop.c:1703
 __blkdev_driver_ioctl block/ioctl.c:224 [inline]
 blkdev_ioctl+0x1cf/0x410 block/ioctl.c:620
 block_ioctl+0x6d/0x80 fs/block_dev.c:1871
 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 0xffff8881299253f0 of 4 bytes by task 5078 on cpu 1:
 disk_max_parts include/linux/genhd.h:232 [inline]
 disk_part_scan_enabled include/linux/genhd.h:239 [inline]
 blkdev_reread_part block/ioctl.c:97 [inline]
 blkdev_common_ioctl+0x55f/0x10b0 block/ioctl.c:549
 blkdev_ioctl+0x167/0x410 block/ioctl.c:618
 block_ioctl+0x6d/0x80 fs/block_dev.c:1871
 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 5078 Comm: systemd-udevd Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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