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BUG: KCSAN: data-race in device_del / mm_update_next_owner

write to 0xffff8881009f202c of 4 bytes by task 1027 on cpu 0:
 memalloc_noio_save include/linux/sched/mm.h:214 [inline]
 device_del+0x123/0x8f0 drivers/base/core.c:3393
 delete_partition block/partitions/core.c:292 [inline]
 blk_drop_partitions+0xf6/0x1a0 block/partitions/core.c:549
 bdev_disk_changed+0x58/0x200 fs/block_dev.c:1248
 __blkdev_get+0x2f9/0x6c0 fs/block_dev.c:1354
 blkdev_get_by_dev+0xa4/0x490 fs/block_dev.c:1458
 blkdev_reread_part block/ioctl.c:100 [inline]
 blkdev_common_ioctl+0xc94/0x1010 block/ioctl.c:508
 blkdev_ioctl+0x16e/0x3c0 block/ioctl.c:577
 block_ioctl+0x6d/0x80 fs/block_dev.c:1671
 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+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881009f202c of 4 bytes by task 24719 on cpu 1:
 mm_update_next_owner+0x1d9/0x520 kernel/exit.c:388
 exit_mm+0x358/0x450 kernel/exit.c:500
 do_exit+0x3ff/0x1560 kernel/exit.c:812
 do_group_exit+0x19b/0x1a0 kernel/exit.c:922
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:933
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:931
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:931
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 24719 Comm: syz-executor.0 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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