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BUG: KCSAN: data-race in _copy_to_iter / fat12_ent_put

write to 0xffff88810c3fd803 of 1 bytes by task 8697 on cpu 0:
 fat12_ent_put+0x7a/0x180 fs/fat/fatent.c:168
 fat_free_clusters+0x2a2/0x790 fs/fat/fatent.c:597
 vfat_mkdir+0xec/0x1e0 fs/fat/namei_vfat.c:886
 vfs_mkdir+0x1ac/0x2b0 fs/namei.c:4120
 do_mkdirat+0xf9/0x260 fs/namei.c:4143
 __do_sys_mkdirat fs/namei.c:4158 [inline]
 __se_sys_mkdirat fs/namei.c:4156 [inline]
 __x64_sys_mkdirat+0x50/0x60 fs/namei.c:4156
 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 0xffff88810c3fd800 of 1024 bytes by task 3949 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:113 [inline]
 copyout lib/iov_iter.c:167 [inline]
 _copy_to_iter+0x12b/0x950 lib/iov_iter.c:316
 copy_page_to_iter+0x171/0x2b0 lib/iov_iter.c:481
 copy_folio_to_iter include/linux/uio.h:185 [inline]
 filemap_read+0x424/0x680 mm/filemap.c:2703
 blkdev_read_iter+0x217/0x2c0 block/fops.c:730
 call_read_iter include/linux/fs.h:1950 [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: 3949 Comm: udevd Not tainted 6.6.0-rc4-syzkaller-00037-g3006adf3be79 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
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