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BUG: KCSAN: data-race in __loop_clr_fd / blkdev_common_ioctl

write to 0xffff8881019da4e0 of 4 bytes by task 24542 on cpu 0:
 __loop_clr_fd+0x5b8/0x640 drivers/block/loop.c:1294
 loop_clr_fd drivers/block/loop.c:1337 [inline]
 lo_ioctl+0x9eb/0x11f0 drivers/block/loop.c:1695
 blkdev_ioctl+0x1d0/0x3c0 block/ioctl.c:585
 block_ioctl+0x6d/0x80 fs/block_dev.c:1664
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881019da4e0 of 4 bytes by task 1033 on cpu 1:
 disk_max_parts include/linux/genhd.h:189 [inline]
 disk_part_scan_enabled include/linux/genhd.h:196 [inline]
 blkdev_reread_part block/ioctl.c:88 [inline]
 blkdev_common_ioctl+0x54c/0x1040 block/ioctl.c:510
 blkdev_ioctl+0x16e/0x3c0 block/ioctl.c:579
 block_ioctl+0x6d/0x80 fs/block_dev.c:1664
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:1069 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:1055
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:1055
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1033 Comm: systemd-udevd Not tainted 5.13.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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