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

write to 0xffff888125486400 of 8 bytes by task 26361 on cpu 1:
 fsync_buffers_list fs/buffer.c:734 [inline]
 sync_mapping_buffers+0x257/0x6e0 fs/buffer.c:563
 fat_file_fsync+0xd4/0x120 fs/fat/file.c:194
 vfs_fsync_range+0x82/0x150 fs/sync.c:197
 generic_write_sync include/linux/fs.h:2856 [inline]
 generic_file_write_iter+0x318/0x38c mm/filemap.c:3474
 call_write_iter include/linux/fs.h:1902 [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+0x530/0x840 fs/splice.c:760
 do_splice_from fs/splice.c:863 [inline]
 direct_splice_actor+0xa0/0xc0 fs/splice.c:1037
 splice_direct_to_actor+0x22b/0x540 fs/splice.c:992
 do_splice_direct+0x161/0x1e0 fs/splice.c:1080
 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/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888125486400 of 8 bytes by task 26357 on cpu 0:
 mark_buffer_dirty_inode+0xa1/0x260 fs/buffer.c:596
 fat12_ent_put+0xf8/0x1b0 fs/fat/fatent.c:171
 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/0xf10 fs/buffer.c:2008
 __block_write_begin fs/buffer.c:2058 [inline]
 block_write_begin+0x77/0x160 fs/buffer.c:2117
 cont_write_begin+0x3d6/0x670 fs/buffer.c:2466
 fat_write_begin+0x72/0xc0 fs/fat/inode.c:235
 pagecache_write_begin+0x6b/0x90 mm/filemap.c:3128
 cont_expand_zero fs/buffer.c:2393 [inline]
 cont_write_begin+0x17a/0x670 fs/buffer.c:2456
 fat_write_begin+0x72/0xc0 fs/fat/inode.c:235
 pagecache_write_begin+0x6b/0x90 mm/filemap.c:3128
 generic_cont_expand_simple+0xb0/0x120 fs/buffer.c:2357
 fat_cont_expand+0x4e/0x1c0 fs/fat/file.c:222
 fat_setattr+0x75d/0x840 fs/fat/file.c:501
 notify_change+0x7e1/0xaa0 fs/attr.c:337
 do_truncate+0xfb/0x180 fs/open.c:64
 do_sys_ftruncate+0x30f/0x340 fs/open.c:195
 __do_sys_ftruncate fs/open.c:205 [inline]
 __se_sys_ftruncate fs/open.c:203 [inline]
 __x64_sys_ftruncate+0x3f/0x50 fs/open.c:203
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 26357 Comm: syz-executor.5 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================