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BUG: KCSAN: data-race in has_bh_in_lru / invalidate_bh_lrus_cpu

write to 0xffff888237d26da0 of 8 bytes by task 26292 on cpu 1:
 __invalidate_bh_lrus fs/buffer.c:1418 [inline]
 invalidate_bh_lrus_cpu+0xad/0xe0 fs/buffer.c:1459
 lru_add_drain_cpu+0x243/0x270 mm/swap.c:645
 lru_add_drain+0x28/0x40 mm/swap.c:724
 exit_mmap+0x199/0x400 mm/mmap.c:3203
 __mmput+0x27/0x1c0 kernel/fork.c:1096
 mmput+0x3d/0x50 kernel/fork.c:1117
 exit_mm+0x350/0x440 kernel/exit.c:502
 do_exit+0x3ff/0x1560 kernel/exit.c:813
 do_group_exit+0xce/0x1a0 kernel/exit.c:923
 get_signal+0xfc3/0x1610 kernel/signal.c:2835
 arch_do_signal_or_restart+0x2a/0x220 arch/x86/kernel/signal.c:789
 handle_signal_work kernel/entry/common.c:148 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:172 [inline]
 exit_to_user_mode_prepare+0x109/0x190 kernel/entry/common.c:209
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888237d26da0 of 8 bytes by task 26293 on cpu 0:
 has_bh_in_lru+0x31/0x1c0 fs/buffer.c:1440
 smp_call_function_many_cond+0x226/0x620 kernel/smp.c:915
 on_each_cpu_cond_mask+0x31/0x40 kernel/smp.c:1133
 on_each_cpu_cond include/linux/smp.h:105 [inline]
 invalidate_bh_lrus+0x26/0x30 fs/buffer.c:1449
 invalidate_bdev+0x4b/0x70 fs/block_dev.c:95
 __loop_clr_fd+0x2e2/0x640 drivers/block/loop.c:1242
 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:1662
 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

value changed: 0xffff888106589478 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 26293 Comm: syz-executor.5 Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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