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BUG: KCSAN: data-race in __lru_add_drain_all / mark_page_accessed

write to 0xffff888237d266a8 of 1 bytes by task 28644 on cpu 1:
 pagevec_add include/linux/pagevec.h:74 [inline]
 pagevec_add_and_need_flush mm/swap.c:244 [inline]
 activate_page mm/swap.c:359 [inline]
 mark_page_accessed+0x36e/0x550 mm/swap.c:444
 shmem_file_read_iter+0x2fd/0x5c0 mm/shmem.c:2644
 call_read_iter include/linux/fs.h:2108 [inline]
 do_iter_readv_writev+0x2e8/0x360 fs/read_write.c:738
 do_iter_read+0x109/0x4b0 fs/read_write.c:801
 vfs_iter_read+0x4c/0x70 fs/read_write.c:843
 lo_read_simple drivers/block/loop.c:361 [inline]
 do_req_filebacked drivers/block/loop.c:637 [inline]
 loop_handle_cmd drivers/block/loop.c:2046 [inline]
 loop_queue_work+0xdeb/0x1310 drivers/block/loop.c:2064
 kthread_worker_fn+0x280/0x4d0 kernel/kthread.c:756
 loop_kthread_worker_fn+0x3e/0x50 drivers/block/loop.c:933
 kthread+0x1d0/0x1f0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff888237d266a8 of 1 bytes by task 28624 on cpu 0:
 pagevec_count include/linux/pagevec.h:61 [inline]
 need_activate_page_drain mm/swap.c:347 [inline]
 __lru_add_drain_all+0x236/0x3e0 mm/swap.c:833
 lru_add_drain_all+0xc/0x10 mm/swap.c:850
 invalidate_bdev+0x50/0x70 fs/block_dev.c:96
 __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: 0x00 -> 0x01

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 28624 Comm: syz-executor.4 Not tainted 5.13.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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