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BUG: KCSAN: data-race in _copy_to_iter / fat16_ent_put

write to 0xffff88813703b240 of 2 bytes by task 5477 on cpu 0:
 fat16_ent_put+0x28/0x60 fs/fat/fatent.c:183
 fat_ent_write+0x62/0xe0 fs/fat/fatent.c:417
 fat_chain_add+0x15f/0x400 fs/fat/misc.c:136
 fat_add_cluster+0x78/0xd0 fs/fat/inode.c:113
 fat_fallocate+0x129/0x1d0 fs/fat/file.c:292
 vfs_fallocate+0x378/0x3e0 fs/open.c:324
 do_vfs_ioctl+0x12d7/0x1390 fs/ioctl.c:849
 __do_sys_ioctl fs/ioctl.c:868 [inline]
 __se_sys_ioctl+0x81/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffff88813703b000 of 1024 bytes by task 3113 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copyout lib/iov_iter.c:167 [inline]
 _copy_to_iter+0x12b/0x910 lib/iov_iter.c:316
 copy_page_to_iter+0x184/0x2c0 lib/iov_iter.c:481
 copy_folio_to_iter include/linux/uio.h:185 [inline]
 filemap_read+0x421/0x670 mm/filemap.c:2709
 blkdev_read_iter+0x217/0x2c0 block/fops.c:616
 call_read_iter include/linux/fs.h:1865 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x3da/0x5c0 fs/read_write.c:470
 ksys_read+0xeb/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+0x42/0x50 fs/read_write.c:621
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 3113 Comm: udevd Not tainted 6.5.0-rc1-syzkaller-00006-g3f01e9fed845 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/03/2023
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