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BUG: KCSAN: data-race in __loop_clr_fd / get_gendisk

write to 0xffff88812a047c18 of 4 bytes by task 7856 on cpu 1:
 __loop_clr_fd+0x474/0x710 drivers/block/loop.c:1193
 loop_clr_fd drivers/block/loop.c:1237 [inline]
 lo_ioctl+0x24a/0xc80 drivers/block/loop.c:1606
 __blkdev_driver_ioctl block/ioctl.c:321 [inline]
 blkdev_ioctl+0x1a1/0x420 block/ioctl.c:717
 block_ioctl+0x91/0xb0 fs/block_dev.c:1983
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x101/0x150 fs/ioctl.c:763
 __do_sys_ioctl fs/ioctl.c:772 [inline]
 __se_sys_ioctl fs/ioctl.c:770 [inline]
 __x64_sys_ioctl+0x47/0x60 fs/ioctl.c:770
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812a047c18 of 4 bytes by task 17447 on cpu 0:
 get_gendisk+0xa3/0x250 block/genhd.c:901
 bdev_get_gendisk fs/block_dev.c:1100 [inline]
 __blkdev_get+0x2d5/0xc40 fs/block_dev.c:1583
 blkdev_get+0x4b/0x210 fs/block_dev.c:1736
 blkdev_open+0x18f/0x1d0 fs/block_dev.c:1875
 do_dentry_open+0x306/0x970 fs/open.c:797
 vfs_open+0x62/0x80 fs/open.c:914
 do_last fs/namei.c:3490 [inline]
 path_openat+0xdbf/0x2f70 fs/namei.c:3607
 do_filp_open+0x11e/0x1b0 fs/namei.c:3637
 do_sys_openat2+0x4f5/0x620 fs/open.c:1149
 do_sys_open+0xa2/0x110 fs/open.c:1165
 ksys_open include/linux/syscalls.h:1386 [inline]
 __do_sys_open fs/open.c:1171 [inline]
 __se_sys_open fs/open.c:1169 [inline]
 __x64_sys_open+0x50/0x60 fs/open.c:1169
 do_syscall_64+0xc7/0x390 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 17447 Comm: blkid Not tainted 5.6.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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