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BUG: KCSAN: data-race in __remove_assoc_queue / mark_buffer_dirty_inode

read to 0xffff888128b062c8 of 8 bytes by task 31449 on cpu 0:
 mark_buffer_dirty_inode+0xa1/0x260 fs/buffer.c:556
 fat16_ent_put+0x82/0x90 fs/fat/fatent.c:182
 fat_alloc_clusters+0x507/0xc40 fs/fat/fatent.c:501
 fat_add_cluster+0x3d/0xd0 fs/fat/inode.c:107
 __fat_get_block fs/fat/inode.c:154 [inline]
 fat_get_block+0x3ae/0x4e0 fs/fat/inode.c:189
 __block_write_begin_int+0x2ea/0xf20 fs/buffer.c:1968
 __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

write to 0xffff888128b062c8 of 8 bytes by task 31453 on cpu 1:
 __remove_assoc_queue+0xa2/0x140 fs/buffer.c:456
 fsync_buffers_list fs/buffer.c:727 [inline]
 sync_mapping_buffers+0x420/0x6e0 fs/buffer.c:523
 fat_file_fsync+0xd4/0x120 fs/fat/file.c:203
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2853 [inline]
 generic_file_write_iter+0x318/0x390 mm/filemap.c:3470
 call_write_iter include/linux/fs.h:1895 [inline]
 do_iter_readv_writev+0x487/0x5b0 fs/read_write.c:693
 do_iter_write fs/read_write.c:970 [inline]
 do_iter_write+0x13b/0x3c0 fs/read_write.c:951
 vfs_iter_write+0x5c/0x80 fs/read_write.c:983
 iter_file_splice_write+0x4c0/0x7f0 fs/splice.c:746
 do_splice_from fs/splice.c:848 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1020
 splice_direct_to_actor+0x215/0x510 fs/splice.c:975
 do_splice_direct+0x161/0x1e0 fs/splice.c:1063
 do_sendfile+0x384/0x7f0 fs/read_write.c:1464
 __do_sys_sendfile64 fs/read_write.c:1519 [inline]
 __se_sys_sendfile64 fs/read_write.c:1511 [inline]
 __x64_sys_sendfile64+0xbe/0x140 fs/read_write.c:1511
 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: 1 PID: 31453 Comm: syz-executor.4 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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