==================================================================
BUG: KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode

write to 0xffff88813a9fe948 of 8 bytes by task 19197 on cpu 0:
 mark_buffer_dirty_inode+0x18b/0x1d0 fs/buffer.c:585
 fat_mirror_bhs+0x205/0x330 fs/fat/fatent.c:397
 fat_alloc_clusters+0x9ad/0xab0 fs/fat/fatent.c:542
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x267/0x610 fs/fat/inode.c:190
 __block_write_begin_int+0x4c5/0x1080 fs/buffer.c:2006
 __block_write_begin fs/buffer.c:2056 [inline]
 block_write_begin fs/buffer.c:2116 [inline]
 cont_write_begin+0x542/0x870 fs/buffer.c:2465
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 generic_perform_write+0x1b8/0x3e0 mm/filemap.c:3770
 __generic_file_write_iter+0x174/0x310 mm/filemap.c:3897
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3929
 call_write_iter include/linux/fs.h:2163 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x7bc/0x900 fs/read_write.c:594
 ksys_write+0xd9/0x190 fs/read_write.c:647
 __do_sys_write fs/read_write.c:659 [inline]
 __se_sys_write fs/read_write.c:656 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:656
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813a9fe948 of 8 bytes by task 19202 on cpu 1:
 mark_buffer_dirty_inode+0x92/0x1d0 fs/buffer.c:581
 fat_mirror_bhs+0x205/0x330 fs/fat/fatent.c:397
 fat_alloc_clusters+0x9ad/0xab0 fs/fat/fatent.c:542
 fat_add_cluster fs/fat/inode.c:108 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x267/0x610 fs/fat/inode.c:190
 __block_write_begin_int+0x4c5/0x1080 fs/buffer.c:2006
 __block_write_begin fs/buffer.c:2056 [inline]
 block_write_begin fs/buffer.c:2116 [inline]
 cont_write_begin+0x542/0x870 fs/buffer.c:2465
 fat_write_begin+0x61/0xf0 fs/fat/inode.c:235
 generic_perform_write+0x1b8/0x3e0 mm/filemap.c:3770
 __generic_file_write_iter+0x174/0x310 mm/filemap.c:3897
 generic_file_write_iter+0x75/0x130 mm/filemap.c:3929
 call_write_iter include/linux/fs.h:2163 [inline]
 do_iter_readv_writev+0x2de/0x380 fs/read_write.c:729
 do_iter_write+0x192/0x5c0 fs/read_write.c:855
 vfs_iter_write+0x4c/0x70 fs/read_write.c:896
 iter_file_splice_write+0x43a/0x790 fs/splice.c:689
 do_splice_from fs/splice.c:767 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:936
 splice_direct_to_actor+0x345/0x650 fs/splice.c:891
 do_splice_direct+0x106/0x190 fs/splice.c:979
 do_sendfile+0x63e/0xbb0 fs/read_write.c:1249
 __do_sys_sendfile64 fs/read_write.c:1314 [inline]
 __se_sys_sendfile64 fs/read_write.c:1300 [inline]
 __x64_sys_sendfile64+0x102/0x140 fs/read_write.c:1300
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x0000000000000000 -> 0xffff88813355ddb0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19202 Comm: syz-executor.5 Not tainted 5.14.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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syz-executor.5 (19202) used greatest stack depth: 10352 bytes left