Re: [PATCH 2/2] mm: Avoid overflows in dirty throttling logic

[Jan Kara <jack@suse.cz>]

On Fri 21-06-24 10:10:58, Andrew Morton wrote:
> On Fri, 21 Jun 2024 16:42:38 +0200 Jan Kara <jack@suse.cz> wrote:
> 
> > The dirty throttling logic is interspersed with assumptions that dirty
> > limits in PAGE_SIZE units fit into 32-bit (so that various
> > multiplications fit into 64-bits). If limits end up being larger, we
> > will hit overflows, possible divisions by 0 etc. Fix these problems by
> > never allowing so large dirty limits as they have dubious practical
> > value anyway. For dirty_bytes / dirty_background_bytes interfaces we can
> > just refuse to set so large limits. For dirty_ratio /
> > dirty_background_ratio it isn't so simple as the dirty limit is computed
> > from the amount of available memory which can change due to memory
> > hotplug etc. So when converting dirty limits from ratios to numbers of
> > pages, we just don't allow the result to exceed UINT_MAX.
> 
> Shouldn't this also be cc:stable?

So this is root-only triggerable problem and kind of "don't do it when it
hurts" issue (who really wants to set dirty limits to > 16 TB?). So I'm not
sure CC stable is warranted but I won't object.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR