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BUG: KCSAN: data-race in device_del / mm_update_next_owner

write to 0xffff888129bb402c of 4 bytes by task 1782 on cpu 1:
 memalloc_noio_save include/linux/sched/mm.h:218 [inline]
 device_del+0x123/0x8f0 drivers/base/core.c:3480
 delete_partition+0x76/0xd0 block/partitions/core.c:295
 blk_drop_partitions+0x7a/0xf0 block/partitions/core.c:546
 bdev_disk_changed+0x13d/0x310 fs/block_dev.c:1252
 __loop_clr_fd+0x51b/0x640 drivers/block/loop.c:1272
 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 0xffff888129bb402c of 4 bytes by task 22189 on cpu 0:
 mm_update_next_owner+0x1d9/0x520 kernel/exit.c:389
 exit_mm+0x358/0x450 kernel/exit.c:501
 do_exit+0x3ff/0x1560 kernel/exit.c:813
 do_group_exit+0x19b/0x1a0 kernel/exit.c:923
 __do_sys_exit_group+0xb/0x10 kernel/exit.c:934
 __se_sys_exit_group+0x5/0x10 kernel/exit.c:932
 __x64_sys_exit_group+0x16/0x20 kernel/exit.c:932
 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: 0 PID: 22189 Comm: syz-executor.2 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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