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BUG: KCSAN: data-race in _copy_to_iter / fat12_ent_put

read-write to 0xffff88811cc2e804 of 1 bytes by task 5800 on cpu 0:
 fat12_ent_put+0xc6/0x180 fs/fat/fatent.c:165
 fat_ent_write+0x5e/0xd0 fs/fat/fatent.c:417
 fat_chain_add+0x15b/0x410 fs/fat/misc.c:136
 fat_add_cluster fs/fat/inode.c:113 [inline]
 __fat_get_block fs/fat/inode.c:155 [inline]
 fat_get_block+0x486/0x600 fs/fat/inode.c:190
 __block_write_begin_int+0x33d/0xc50 fs/buffer.c:1991
 __block_write_begin fs/buffer.c:2041 [inline]
 block_write_begin+0x73/0x170 fs/buffer.c:2102
 cont_write_begin+0x3f1/0x520 fs/buffer.c:2456
 fat_write_begin+0x5d/0xe0 fs/fat/inode.c:235
 generic_perform_write+0x1d4/0x3f0 mm/filemap.c:3753
 __generic_file_write_iter+0xe3/0x280 mm/filemap.c:3881
 generic_file_write_iter+0x79/0x1c0 mm/filemap.c:3913
 do_iter_write+0x494/0x750 fs/read_write.c:861
 vfs_iter_write+0x4c/0x70 fs/read_write.c:902
 iter_file_splice_write+0x44a/0x7c0 fs/splice.c:686
 do_splice_from fs/splice.c:764 [inline]
 direct_splice_actor+0x80/0xa0 fs/splice.c:931
 splice_direct_to_actor+0x305/0x620 fs/splice.c:886
 do_splice_direct+0xfb/0x180 fs/splice.c:974
 do_sendfile+0x3bf/0x910 fs/read_write.c:1255
 __do_sys_sendfile64 fs/read_write.c:1323 [inline]
 __se_sys_sendfile64 fs/read_write.c:1309 [inline]
 __x64_sys_sendfile64+0x10c/0x150 fs/read_write.c:1309
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88811cc2e800 of 1024 bytes by task 3077 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:120 [inline]
 copyout lib/iov_iter.c:169 [inline]
 _copy_to_iter+0x116/0x8e0 lib/iov_iter.c:527
 copy_page_to_iter+0x333/0x3f0 lib/iov_iter.c:725
 copy_folio_to_iter include/linux/uio.h:169 [inline]
 filemap_read+0x11db/0x1510 mm/filemap.c:2726
 blkdev_read_iter+0x2c6/0x370 block/fops.c:598
 call_read_iter include/linux/fs.h:2185 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x3a5/0x560 fs/read_write.c:470
 ksys_read+0xe8/0x1a0 fs/read_write.c:613
 __do_sys_read fs/read_write.c:623 [inline]
 __se_sys_read fs/read_write.c:621 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3077 Comm: udevd Not tainted 6.1.0-rc1-syzkaller-00249-g4da34b7d175d-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
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