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BUG: KCSAN: data-race in fat_bmap / generic_write_end

write to 0xffff8881069b1c30 of 8 bytes by task 13909 on cpu 0:
 i_size_write include/linux/fs.h:934 [inline]
 generic_write_end+0x94/0x230 fs/buffer.c:2275
 fat_write_end+0x4e/0x160 fs/fat/inode.c:244
 generic_perform_write+0x267/0x410 mm/filemap.c:3941
 __generic_file_write_iter+0xec/0x120 mm/filemap.c:4022
 generic_file_write_iter+0x7d/0x1c0 mm/filemap.c:4051
 call_write_iter include/linux/fs.h:2087 [inline]
 iter_file_splice_write+0x5de/0x950 fs/splice.c:743
 do_splice_from fs/splice.c:941 [inline]
 direct_splice_actor+0x167/0x2c0 fs/splice.c:1164
 splice_direct_to_actor+0x2fb/0x660 fs/splice.c:1108
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0xd7/0x150 fs/splice.c:1233
 do_sendfile+0x3b9/0x960 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1362 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1348
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

read to 0xffff8881069b1c30 of 8 bytes by task 13921 on cpu 1:
 i_size_read include/linux/fs.h:912 [inline]
 is_exceed_eof fs/fat/cache.c:340 [inline]
 fat_bmap+0x1d2/0x290 fs/fat/cache.c:375
 __fat_get_block fs/fat/inode.c:129 [inline]
 fat_get_block+0xd1/0x5e0 fs/fat/inode.c:190
 do_mpage_readpage+0x47b/0xca0 fs/mpage.c:232
 mpage_readahead+0x1ad/0x2d0 fs/mpage.c:381
 fat_readahead+0x1c/0x20 fs/fat/inode.c:210
 read_pages+0x9f/0x540 mm/readahead.c:160
 page_cache_ra_unbounded+0x224/0x2e0
 do_page_cache_ra mm/readahead.c:299 [inline]
 page_cache_ra_order mm/readahead.c:544 [inline]
 ondemand_readahead+0x50b/0x670 mm/readahead.c:666
 page_cache_sync_ra+0x27e/0x2a0 mm/readahead.c:693
 page_cache_sync_readahead include/linux/pagemap.h:1300 [inline]
 filemap_get_pages+0x251/0xf90 mm/filemap.c:2498
 filemap_splice_read+0x337/0x8f0 mm/filemap.c:2872
 do_splice_read fs/splice.c:985 [inline]
 splice_direct_to_actor+0x268/0x660 fs/splice.c:1089
 do_splice_direct_actor fs/splice.c:1207 [inline]
 do_splice_direct+0xd7/0x150 fs/splice.c:1233
 do_sendfile+0x3b9/0x960 fs/read_write.c:1295
 __do_sys_sendfile64 fs/read_write.c:1362 [inline]
 __se_sys_sendfile64 fs/read_write.c:1348 [inline]
 __x64_sys_sendfile64+0x110/0x150 fs/read_write.c:1348
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x1d0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

value changed: 0x0000000000299000 -> 0x000000000029a000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 13921 Comm: syz-executor.3 Not tainted 6.8.0-rc5-syzkaller-00163-gffd2cb6b718e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
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