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BUG: KCSAN: data-race in _copy_to_iter / fat16_ent_put

write to 0xffff88815e889264 of 2 bytes by task 27238 on cpu 1:
 fat16_ent_put+0x24/0x50 fs/fat/fatent.c:183
 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/0xc70 fs/buffer.c:2006
 __block_write_begin fs/buffer.c:2056 [inline]
 block_write_begin+0x73/0x170 fs/buffer.c:2117
 cont_write_begin+0x3f1/0x520 fs/buffer.c:2471
 fat_write_begin+0x5d/0xe0 fs/fat/inode.c:235
 generic_perform_write+0x1d4/0x3f0 mm/filemap.c:3745
 __generic_file_write_iter+0xe3/0x280 mm/filemap.c:3873
 generic_file_write_iter+0x79/0x1c0 mm/filemap.c:3905
 call_write_iter include/linux/fs.h:2190 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x468/0x760 fs/read_write.c:584
 ksys_write+0xe8/0x1a0 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:646
 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 0xffff88815e889000 of 1377 bytes by task 10133 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:169 [inline]
 _copy_to_iter+0x11d/0x8b0 lib/iov_iter.c:524
 copy_page_to_iter+0x333/0x3f0 lib/iov_iter.c:722
 copy_folio_to_iter include/linux/uio.h:169 [inline]
 filemap_read+0x11fb/0x1490 mm/filemap.c:2718
 blkdev_read_iter+0x2c6/0x370 block/fops.c:598
 call_read_iter include/linux/fs.h:2184 [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: 0 PID: 10133 Comm: udevd Not tainted 6.0.0-syzkaller-09039-ga6afa4199d3d-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
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I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
I/O error, dev loop5, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
I/O error, dev loop3, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 2
I/O error, dev loop3, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 2
buffer_io_error: 5 callbacks suppressed
Buffer I/O error on dev loop3, logical block 0, async page read