Re: [PATCH] mm/vmstat: Reduce zone lock hold time when reading /proc/pagetypeinfo

From: Qian Cai
Date: Thu Oct 24 2019 - 01:33:07 EST

> On Oct 23, 2019, at 6:30 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> Yes, removing things is hard. One approach is to add printk_once(this
> is going away, please email us if you use it) then wait a few years.
> Backport that one-liner into -stable kernels to hopefully speed up the
> process.

Although it still look like an overkill to me given,

1) Mel given a green light to remove it.
2) Nobody justifies any sensible reason to keep it apart from it was probably only triggering by some testing tools blindly read procfs entries.

it is still better than wasting developersâ time to beating the âdeadâ horse.

> Meanwhile, we need to fix the DoS opportunity. How about my suggestion
> that we limit the count to 1024, see if anyone notices? I bet they
> don't!

The DoS is probably there since the file had been introduced almost 10 years ago, so I suspect it is not that easily exploitable.