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BUG: KCSAN: data-race in clean_buffers / recalc_bh_state

read to 0xffffffff86052650 of 4 bytes by task 2611 on cpu 1:
 clean_buffers fs/mpage.c:482 [inline]
 clean_buffers+0x104/0x1b0 fs/mpage.c:461
 __mpage_writepage+0xad1/0xe70 fs/mpage.c:657
 write_cache_pages+0x47a/0xb40 mm/page-writeback.c:2238
 mpage_writepages+0xab/0x180 fs/mpage.c:730
 fat_writepages+0x2e/0x40 fs/fat/inode.c:204
 do_writepages+0x6b/0x170 mm/page-writeback.c:2344
 __writeback_single_inode+0xaf/0x8e0 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x4ba/0xa50 fs/fs-writeback.c:1716
 wb_writeback+0x1f9/0x6a0 fs/fs-writeback.c:1892
 wb_do_writeback fs/fs-writeback.c:2037 [inline]
 wb_workfn+0x22e/0x970 fs/fs-writeback.c:2078
 process_one_work+0x3d4/0x890 kernel/workqueue.c:2269
 worker_thread+0xa0/0x800 kernel/workqueue.c:2415
 kthread+0x1d4/0x200 drivers/block/aoe/aoecmd.c:1253
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

write to 0xffffffff86052650 of 4 bytes by task 8654 on cpu 0:
 recalc_bh_state fs/buffer.c:3363 [inline]
 recalc_bh_state+0x124/0x150 fs/buffer.c:3353
 alloc_buffer_head+0xa8/0x100 fs/buffer.c:3373
 alloc_page_buffers+0x13d/0x340 fs/buffer.c:831
 create_empty_buffers+0x47/0x3e0 fs/buffer.c:1518
 create_page_buffers+0x15a/0x180 fs/buffer.c:1635
 __block_write_begin_int+0x14d/0xf20 fs/buffer.c:1947
 __block_write_begin fs/buffer.c:2018 [inline]
 block_write_begin+0x77/0x160 fs/buffer.c:2077
 cont_write_begin+0x3d6/0x670 fs/buffer.c:2426
 fat_write_begin+0x72/0xc0 fs/fat/inode.c:235
 pagecache_write_begin+0x6b/0x90 mm/filemap.c:3149
 cont_expand_zero fs/buffer.c:2353 [inline]
 cont_write_begin+0x17a/0x670 fs/buffer.c:2416
 fat_write_begin+0x72/0xc0 fs/fat/inode.c:235
 pagecache_write_begin+0x6b/0x90 mm/filemap.c:3149
 generic_cont_expand_simple+0xb0/0x120 fs/buffer.c:2317
 fat_cont_expand+0x4e/0x1c0 fs/fat/file.c:233
 fat_fallocate+0x1af/0x1f0 fs/fat/file.c:311
 vfs_fallocate+0x3be/0x650 fs/open.c:309
 ksys_fallocate+0x61/0xa0 fs/open.c:332
 __do_sys_fallocate fs/open.c:340 [inline]
 __se_sys_fallocate fs/open.c:338 [inline]
 __x64_sys_fallocate+0x5e/0x80 fs/open.c:338
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 8654 Comm: syz-executor.5 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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