On 1/23/18 10:20 AM, Eryu Guan wrote:

Attributes that only implement .seq_ops are read-only, any write to
them should be rejected. But currently kernel would crash when
writing to such debugfs entries, e.g.

chmod +w /sys/kernel/debug/block/<dev>/requeue_list
echo 0 > /sys/kernel/debug/block/<dev>/requeue_list
chmod -w /sys/kernel/debug/block/<dev>/requeue_list

Fix it by returning -EPERM in blk_mq_debugfs_write() when writing to
such attributes.

I don't particularly like the fix, since it's not really clear why
that comparison makes sense. Can't we just prevent anyone from
making the debugfs entries writable? Seems like a much more sane
approach.

-- 
Jens Axboe