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BUG: KCSAN: data-race in copy_page_to_iter / fat_alloc_new_dir

write to 0xffff88810664c02b of 1 bytes by task 6736 on cpu 1:
 fat_alloc_new_dir+0x1fc/0x500 fs/fat/dir.c:1163
 vfat_mkdir+0x81/0x230 fs/fat/namei_vfat.c:861
 vfs_mkdir+0x2c3/0x3e0 fs/namei.c:3885
 do_mkdirat+0x12e/0x2c0 fs/namei.c:3911
 __do_sys_mkdirat fs/namei.c:3926 [inline]
 __se_sys_mkdirat fs/namei.c:3924 [inline]
 __x64_sys_mkdirat+0x4c/0x60 fs/namei.c:3924
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810664c000 of 256 bytes by task 6740 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:156 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:228 [inline]
 __copy_page_to_iter lib/iov_iter.c:805 [inline]
 copy_page_to_iter+0x2cb/0x950 lib/iov_iter.c:833
 filemap_read+0xee6/0x1220 mm/filemap.c:2683
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2779
 blkdev_read_iter+0xb9/0xf0 block/fops.c:544
 call_read_iter include/linux/fs.h:2157 [inline]
 new_sync_read fs/read_write.c:404 [inline]
 vfs_read+0x66c/0x750 fs/read_write.c:485
 ksys_read+0xd9/0x190 fs/read_write.c:623
 __do_sys_read fs/read_write.c:633 [inline]
 __se_sys_read fs/read_write.c:631 [inline]
 __x64_sys_read+0x3e/0x50 fs/read_write.c:631
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x44/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 6740 Comm: systemd-udevd Not tainted 5.15.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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