[External] Re: [PATCH] mempool: fix rte_mempool_avail_count may segment fault when used in multiprocess

[David Marchand]

On Tue, Nov 15, 2022 at 2:51 AM Fengnan Chang
<changfengnan at bytedance.com> wrote:
>
> David Marchand <david.marchand at redhat.com> 于2022年11月15日周二 04:44写道：
> >
> > On Mon, Nov 14, 2022 at 9:13 AM changfengnan <changfengnan at bytedance.com> wrote:
> > >
> > > rte_mempool_create put tailq entry into rte_mempool_tailq list before
> > > populate, and pool_data set when populate. So in multi process, if
> > > process A create mempool, and process B can get mempool through
> > > rte_mempool_lookup before pool_data set, if B call rte_mempool_lookup,
> > > it will cause segment fault.
> >
> > I fail to see how pool_data impacts rte_mempool_lookup.
> > Something is fishy about this commitlog.
>
> oh, it's my fault about this commit. correct: if B can get mempool through
> rte_mempool_lookup before pool_data set, and call rte_mempool_avail_count,
> it will cause segment fault.

Ok, now it makes more sense :-).

>
> >
> >
> > > Fix this by put tailq entry into rte_mempool_tailq after populate.
> >
> > Moving tailq manipulation to rte_mempool_create only, is probably incorrect.
> > An application is allowed to call rte_mempool_create_empty() and
> > rte_mempool_populate().
> >
> > I did not look in depth, but It is likely the reason why testpmd (as
> > run with devtools/test-null.sh) won't pass anymore.
> > The CI reported this issue in various envs.
> >
> > We can't take this patch.
>
> Yeah, this version makes CI fail.
> I didn't notice rte_mempool_create_empty will called directly before, maybe
> add a new flag bit to indicate when to put tailq entry into rte_mempool_tailq
> list is a better way. If no better idea, I'll send a new version.

I don't think we need an other flag.
Can we "publish" the mempool at the mempool_ops_alloc_once stage?


>
> >
> >
> > >
> > > Signed-off-by: changfengnan <changfengnan at bytedance.com>
> >
> > Please use your real name.
>
> It's my real name.

Sorry, I meant your full name, like Fengnan Chang <changfengnan at bytedance.com>


-- 
David Marchand