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BUG: KCSAN: data-race in copy_page_to_iter / fat_alloc_new_dir

write to 0xffff888130f82e2b of 1 bytes by task 10969 on cpu 1:
 fat_alloc_new_dir+0x1ab/0x4b0 fs/fat/dir.c:1163
 vfat_mkdir+0x70/0x210 fs/fat/namei_vfat.c:860
 vfs_mkdir+0x288/0x350 fs/namei.c:3650
 do_mkdirat+0x132/0x220 fs/namei.c:3673
 __do_sys_mkdirat fs/namei.c:3684 [inline]
 __se_sys_mkdirat fs/namei.c:3682 [inline]
 __x64_sys_mkdirat+0x3e/0x50 fs/namei.c:3682
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff888130f82000 of 4096 bytes by task 10973 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:147 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:219 [inline]
 copy_page_to_iter+0x334/0x850 lib/iov_iter.c:926
 generic_file_buffered_read+0x14d0/0x2110 mm/filemap.c:2332
 generic_file_read_iter+0x80/0x3d0 mm/filemap.c:2535
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1925
 call_read_iter include/linux/fs.h:1897 [inline]
 new_sync_read fs/read_write.c:415 [inline]
 vfs_read+0x552/0x5c0 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+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 10973 Comm: systemd-udevd Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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