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From: David Marchand <david.marchand@redhat.com>
Date: Fri, 17 Mar 2023 19:51:25 +0100
Message-ID: <CAJFAV8zAfOFpK8JpR_f_VGV43XfMGkRF_EL1o2xOo5FRShDSXA@mail.gmail.com>
Subject: Re: [PATCH v5 2/2] eal: fix failure path race setting new thread
affinity
To: Tyler Retzlaff <roretzla@linux.microsoft.com>
Cc: dev@dpdk.org, thomas@monjalon.net, stephen@networkplumber.org,
stable@dpdk.org, Dodji Seketeli <dodji@redhat.com>
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On Fri, Mar 17, 2023 at 3:50=E2=80=AFPM Tyler Retzlaff
<roretzla@linux.microsoft.com> wrote:
> > > -struct thread_routine_ctx {
> > > +struct thread_start_context {
> > > rte_thread_func thread_func;
> > > - void *routine_args;
> > > + void *thread_args;
> > > + const rte_thread_attr_t *thread_attr;
> > > + pthread_mutex_t wrapper_mutex;
> > > + pthread_cond_t wrapper_cond;
> > > + int wrapper_ret;
> > > + volatile int wrapper_done;
> >
> > One question.
> >
> > I see that wrapper_done is accessed under wrapper_mutex.
> > Is volatile needed?
>
> I'm not entirely certain. i'm being cautious since i can conceive of the
> load in the loop being optimized as a single load by the compiler. but
> again i'm not sure, i always like to learn if someone knows better.
After an interesting discussion with Dodji on C99 and side effects
(5.1.2.3/2 and 5.1.2.3/3), I am a bit more convinced that we don't
need this volatile.
>
> >
> > (nit: a boolean is probably enough too)
>
> I have no issue with it being a _Bool if you want to adjust it for that
> i certainly don't object. ordinarily i would use _Bool but a lot of dpdk
> code seems to prefer int so that's why i chose it. if we use the macro
> bool then we should include stdbool.h directly into this translation
> unit.
>
> >
> > I was thinking of squashing below diff:
>
> Yeah, no objection. you can decide if you want to keep the volatile or
> not and add the stdbool.h include.
>
> Thanks for reviewing, appreciate it.
This is a fix but this v5 had an additional change in affinity setting
(switching to rte_thread_set_affinity()).
To be on the safe side wrt backport, I'll also revert to calling
rte_thread_set_affinity_by_id as this is what was being used before.
And this removes the need for patch 1.
Sending a v6 soon, so that it goes through the CI before rc3.
--=20
David Marchand