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BUG: KCSAN: data-race in fat_bmap / generic_write_end

write to 0xffff88812ae0e990 of 8 bytes by task 13760 on cpu 1:
 i_size_write include/linux/fs.h:871 [inline]
 generic_write_end+0x98/0x250 fs/buffer.c:2186
 fat_write_end+0x4a/0x150 fs/fat/inode.c:249
 generic_perform_write+0x23e/0x3a0 mm/filemap.c:3536
 __generic_file_write_iter+0x225/0x330 mm/filemap.c:3622
 generic_file_write_iter+0x309/0x3f0 mm/filemap.c:3686
 call_write_iter include/linux/fs.h:1887 [inline]
 do_iter_readv_writev+0x2cb/0x360 fs/read_write.c:721
 do_iter_write+0x112/0x4b0 fs/read_write.c:847
 vfs_iter_write+0x4c/0x70 fs/read_write.c:888
 iter_file_splice_write+0x42a/0x780 fs/splice.c:769
 do_splice_from fs/splice.c:865 [inline]
 direct_splice_actor+0x95/0x150 fs/splice.c:1035
 splice_direct_to_actor+0x365/0x660 fs/splice.c:990
 do_splice_direct+0xf5/0x170 fs/splice.c:1078
 do_sendfile+0x574/0xb70 fs/read_write.c:1238
 __do_sys_sendfile64 fs/read_write.c:1299 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1285
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812ae0e990 of 8 bytes by task 13751 on cpu 0:
 i_size_read include/linux/fs.h:849 [inline]
 is_exceed_eof fs/fat/cache.c:340 [inline]
 fat_bmap+0x1cb/0x290 fs/fat/cache.c:375
 __fat_get_block fs/fat/inode.c:129 [inline]
 fat_get_block+0xa2/0x5a0 fs/fat/inode.c:190
 do_mpage_readpage+0x422/0x1030 fs/mpage.c:231
 mpage_readahead+0x157/0x340 fs/mpage.c:391
 fat_readahead+0x18/0x20 fs/fat/inode.c:215
 read_pages+0xa0/0x6e0 mm/readahead.c:130
 page_cache_ra_unbounded+0x464/0x4c0 mm/readahead.c:238
 ondemand_readahead+0x560/0x780 mm/readahead.c:267
 page_cache_sync_ra+0x145/0x170 mm/readahead.c:569
 page_cache_sync_readahead include/linux/pagemap.h:839 [inline]
 generic_file_buffered_read+0x315/0x20b0 mm/filemap.c:2219
 generic_file_read_iter+0x80/0x3d0 mm/filemap.c:2527
 call_read_iter include/linux/fs.h:1881 [inline]
 generic_file_splice_read+0x22a/0x310 fs/splice.c:311
 do_splice_to fs/splice.c:889 [inline]
 splice_direct_to_actor+0x2ab/0x660 fs/splice.c:969
 do_splice_direct+0xf5/0x170 fs/splice.c:1078
 do_sendfile+0x574/0xb70 fs/read_write.c:1238
 __do_sys_sendfile64 fs/read_write.c:1299 [inline]
 __se_sys_sendfile64 fs/read_write.c:1285 [inline]
 __x64_sys_sendfile64+0xf2/0x130 fs/read_write.c:1285
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13751 Comm: syz-executor.5 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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