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BUG: KCSAN: data-race in write_cache_pages / write_cache_pages

write to 0xffff888101b8c638 of 8 bytes by task 1825 on cpu 0:
 write_cache_pages+0x7a4/0x7f0 mm/page-writeback.c:2306
 generic_writepages+0x7c/0xc0 mm/page-writeback.c:2346
 blkdev_writepages+0x19/0x20 block/fops.c:430
 do_writepages+0x1cb/0x330 mm/page-writeback.c:2364
 filemap_fdatawrite_wbc mm/filemap.c:384 [inline]
 __filemap_fdatawrite_range mm/filemap.c:417 [inline]
 __filemap_fdatawrite mm/filemap.c:423 [inline]
 filemap_flush+0xd9/0x100 mm/filemap.c:450
 sync_blockdev_nowait+0x32/0x40 block/bdev.c:187
 sync_filesystem+0xdc/0x180 fs/sync.c:60
 generic_shutdown_super+0x40/0x250 fs/super.c:445
 kill_block_super+0x4a/0x90 fs/super.c:1394
 deactivate_locked_super+0x6a/0xb0 fs/super.c:332
 deactivate_super+0x85/0x90 fs/super.c:363
 cleanup_mnt+0x267/0x2d0 fs/namespace.c:1173
 __cleanup_mnt+0x15/0x20 fs/namespace.c:1180
 task_work_run+0x8e/0x110 kernel/task_work.c:164
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
 exit_to_user_mode_prepare+0x160/0x190 kernel/entry/common.c:207
 __syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:300
 do_syscall_64+0x50/0xd0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x44/0xae

write to 0xffff888101b8c638 of 8 bytes by task 1844 on cpu 1:
 write_cache_pages+0x7a4/0x7f0 mm/page-writeback.c:2306
 generic_writepages+0x7c/0xc0 mm/page-writeback.c:2346
 blkdev_writepages+0x19/0x20 block/fops.c:430
 do_writepages+0x1cb/0x330 mm/page-writeback.c:2364
 __writeback_single_inode+0x81/0x590 fs/fs-writeback.c:1618
 writeback_sb_inodes+0x677/0xdf0 fs/fs-writeback.c:1891
 __writeback_inodes_wb+0xb0/0x2b0 fs/fs-writeback.c:1961
 wb_writeback+0x280/0x650 fs/fs-writeback.c:2066
 wb_check_background_flush fs/fs-writeback.c:2132 [inline]
 wb_do_writeback+0x51d/0x560 fs/fs-writeback.c:2220
 wb_workfn+0xc8/0x440 fs/fs-writeback.c:2248
 process_one_work+0x3f6/0x960 kernel/workqueue.c:2307
 worker_thread+0x616/0xa70 kernel/workqueue.c:2454
 kthread+0x1bf/0x1e0 kernel/kthread.c:377
 ret_from_fork+0x1f/0x30

value changed: 0x0000000000000000 -> 0x0000000000000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1844 Comm: kworker/u4:4 Not tainted 5.17.0-rc6-syzkaller-00251-gdcde98da9970-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-7:4)
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