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BUG: KCSAN: data-race in _copy_to_iter / fat12_ent_put

read-write to 0xffff88812774e20d of 1 bytes by task 18573 on cpu 1:
 fat12_ent_put+0xcc/0x180 fs/fat/fatent.c:165
 fat_alloc_clusters+0x4b5/0xa60 fs/fat/fatent.c:503
 fat_alloc_new_dir+0xbe/0x510 fs/fat/dir.c:1144
 vfat_mkdir+0x9a/0x1e0 fs/fat/namei_vfat.c:859
 vfs_mkdir+0x1ac/0x2b0 fs/namei.c:4117
 do_mkdirat+0xf9/0x260 fs/namei.c:4140
 __do_sys_mkdir fs/namei.c:4160 [inline]
 __se_sys_mkdir fs/namei.c:4158 [inline]
 __x64_sys_mkdir+0x44/0x50 fs/namei.c:4158
 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 0xffff88812774e000 of 1024 bytes by task 5636 on cpu 0:
 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: 0 PID: 5636 Comm: udevd Not tainted 6.4.0-syzkaller-12155-ga452483508d7 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
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