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BUG: KCSAN: data-race in _copy_to_iter / fat16_ent_put

write to 0xffff88813dc7d3ee of 2 bytes by task 30096 on cpu 1:
 fat16_ent_put+0x28/0x60 fs/fat/fatent.c:183
 fat_ent_write+0x66/0xe0 fs/fat/fatent.c:417
 fat_chain_add+0x15f/0x400 fs/fat/misc.c:136
 fat_add_cluster fs/fat/inode.c:112 [inline]
 __fat_get_block fs/fat/inode.c:154 [inline]
 fat_get_block+0x46b/0x5e0 fs/fat/inode.c:189
 __block_write_begin_int+0x417/0xfa0 fs/buffer.c:2116
 block_write_begin fs/buffer.c:2226 [inline]
 cont_write_begin+0x546/0x860 fs/buffer.c:2577
 fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
 cont_expand_zero fs/buffer.c:2504 [inline]
 cont_write_begin+0x18b/0x860 fs/buffer.c:2567
 fat_write_begin+0x51/0xe0 fs/fat/inode.c:228
 generic_cont_expand_simple+0xaa/0x150 fs/buffer.c:2468
 fat_cont_expand+0x3a/0x160 fs/fat/file.c:223
 fat_setattr+0x2aa/0x840 fs/fat/file.c:513
 notify_change+0x85c/0x8e0 fs/attr.c:552
 do_truncate fs/open.c:65 [inline]
 do_ftruncate+0x3cf/0x460 fs/open.c:181
 do_sys_ftruncate fs/open.c:196 [inline]
 __do_sys_ftruncate fs/open.c:201 [inline]
 __se_sys_ftruncate fs/open.c:199 [inline]
 __x64_sys_ftruncate+0x67/0xc0 fs/open.c:199
 x64_sys_call+0x9d9/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:78
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88813dc7d000 of 1024 bytes by task 12137 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:300 [inline]
 iterate_and_advance include/linux/iov_iter.h:328 [inline]
 _copy_to_iter+0x130/0xd00 lib/iov_iter.c:185
 copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:362
 copy_folio_to_iter include/linux/uio.h:189 [inline]
 filemap_read+0x42d/0x6a0 mm/filemap.c:2697
 blkdev_read_iter+0x20e/0x2c0 block/fops.c:770
 new_sync_read fs/read_write.c:484 [inline]
 vfs_read+0x5dc/0x700 fs/read_write.c:565
 ksys_read+0xe8/0x1b0 fs/read_write.c:708
 __do_sys_read fs/read_write.c:717 [inline]
 __se_sys_read fs/read_write.c:715 [inline]
 __x64_sys_read+0x42/0x50 fs/read_write.c:715
 x64_sys_call+0x2874/0x2dc0 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 12137 Comm: udevd Tainted: G        W          6.13.0-rc1-syzkaller-00025-gfeffde684ac2 #0
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
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