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BUG: KCSAN: data-race in copy_page_to_iter / ext4_fill_super

write to 0xffff88813bf57410 of 4 bytes by task 11782 on cpu 1:
 ext4_fill_super+0x688f/0x7f90 fs/ext4/super.c:5005
 mount_bdev+0x1e8/0x290 fs/super.c:1367
 ext4_mount+0x2d/0x40 fs/ext4/super.c:6605
 legacy_get_tree+0x70/0xc0 fs/fs_context.c:592
 vfs_get_tree+0x4a/0x1a0 fs/super.c:1497
 do_new_mount fs/namespace.c:2903 [inline]
 path_mount+0x11d6/0x1ce0 fs/namespace.c:3233
 do_mount fs/namespace.c:3246 [inline]
 __do_sys_mount fs/namespace.c:3454 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3431
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3431
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813bf57400 of 1024 bytes by task 11780 on cpu 0:
 instrument_copy_to_user include/linux/instrumented.h:119 [inline]
 copyout lib/iov_iter.c:145 [inline]
 copy_page_to_iter_iovec lib/iov_iter.c:217 [inline]
 copy_page_to_iter+0x31b/0x860 lib/iov_iter.c:912
 filemap_read+0xee6/0x1210 mm/filemap.c:2519
 generic_file_read_iter+0x84/0x3e0 mm/filemap.c:2615
 blkdev_read_iter+0xb3/0xc0 fs/block_dev.c:1727
 call_read_iter include/linux/fs.h:1971 [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+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11780 Comm: systemd-udevd Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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