linux-kernel - RE: [PATCH 1/3] perf: convert perf_event_context.refcount to refcount

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Message-ID: <2236FBA76BA1254E88B949DDB74E612BA4B9DD52@IRSMSX102.ger.corp.intel.com>
Date:   Fri, 1 Feb 2019 15:44:38 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Mark Rutland <mark.rutland@....com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>
Subject: RE: [PATCH 1/3] perf: convert perf_event_context.refcount to
 refcount_t

> On Tue, Jan 29, 2019 at 01:55:32PM +0000, Reshetova, Elena wrote:
> > > On Mon, Jan 28, 2019 at 02:27:26PM +0200, Elena Reshetova wrote:
> > > > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > > > index 3cd13a3..a1e87d2 100644
> > > > --- a/kernel/events/core.c
> > > > +++ b/kernel/events/core.c
> > > > @@ -1171,7 +1171,7 @@ static void perf_event_ctx_deactivate(struct
> > > perf_event_context *ctx)
> > > >
> > > >  static void get_ctx(struct perf_event_context *ctx)
> > > >  {
> > > > -	WARN_ON(!atomic_inc_not_zero(&ctx->refcount));
> > > > +	WARN_ON(!refcount_inc_not_zero(&ctx->refcount));
> > >
> > > This could be refcount_inc(), remember how that already produces a WARN
> > > when we try and increment 0.
> >
> > But is this true for the x86 arch-specific implementation also?
> 
> If you use recount_inc_checked(), it will always produce the WARN(),
> even when using the x86-specific refcount implementation.
> 
> (this was one place I had intended to use the *_checked() forms of the
> refcount ops).

Yes, with refcount_inc_checked() it would work, but I don't like it
that much when we have functions that behave regardless of refcount 
config. It does help for code minimization & clarity like here, but I think 
it complicates things even more: two different configs, then functions that
do not obey configs, etc. 

Anyhow, I can change this to refcount_inc_checked(), if this is what everyone
thinks is the best. 

Best Regards,
Elena.