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BUG: KCSAN: data-race in copy_page_to_iter / fat12_ent_put

write to 0xffff888134fa2204 of 1 bytes by task 15734 on cpu 0:
 fat12_ent_put+0xce/0x1b0 fs/fat/fatent.c:163
 fat_alloc_clusters+0x430/0xa50 fs/fat/fatent.c:501
 fat_alloc_new_dir+0x63/0x4b0 fs/fat/dir.c:1144
 vfat_mkdir+0x70/0x210 fs/fat/namei_vfat.c:861
 vfs_mkdir+0x2a4/0x370 fs/namei.c:3813
 do_mkdirat+0x11d/0x200 fs/namei.c:3838
 __do_sys_mkdirat fs/namei.c:3851 [inline]
 __se_sys_mkdirat fs/namei.c:3849 [inline]
 __x64_sys_mkdirat+0x3e/0x50 fs/namei.c:3849
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888134fa2000 of 1024 bytes by task 15731 on cpu 1:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:189 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:261 [inline]
 copy_page_to_iter+0x320/0x860 lib/iov_iter.c:973
 filemap_read+0xf06/0x1230 mm/filemap.c:2605
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2701
 blkdev_read_iter+0xb9/0xf0 fs/block_dev.c:1730
 call_read_iter include/linux/fs.h:2108 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x565/0x5d0 fs/read_write.c:496
 ksys_read+0xce/0x180 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:642
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 15731 Comm: systemd-udevd Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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