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BUG: KCSAN: data-race in copy_page_to_iter / ext4_setup_super

write to 0xffff88813d41943a of 2 bytes by task 26379 on cpu 0:
 ext4_setup_super+0x23f/0x4d0 fs/ext4/super.c:2685
 ext4_fill_super+0x5750/0x7ff0 fs/ext4/super.c:4976
 mount_bdev+0x1e8/0x290 fs/super.c:1368
 ext4_mount+0x2d/0x40 fs/ext4/super.c:6638
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:610
 vfs_get_tree+0x4a/0x1a0 fs/super.c:1498
 do_new_mount fs/namespace.c:2923 [inline]
 path_mount+0x11f2/0x1d30 fs/namespace.c:3253
 do_mount fs/namespace.c:3266 [inline]
 __do_sys_mount fs/namespace.c:3474 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3451
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3451
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813d419400 of 1024 bytes by task 26376 on cpu 1:
 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:801 [inline]
 copy_page_to_iter+0x2e1/0x940 lib/iov_iter.c:829
 filemap_read+0xef6/0x1220 mm/filemap.c:2605
 generic_file_read_iter+0x75/0x2c0 mm/filemap.c:2701
 blkdev_read_iter+0xb9/0xf0 fs/block_dev.c:1671
 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_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 26376 Comm: systemd-udevd Tainted: G        W         5.14.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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