linux-kernel - Re: [PATCH] perf: drop module reference on event init failure

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Date:	Fri, 16 Jan 2015 13:49:42 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH] perf: drop module reference on event init failure

On Fri, Jan 16, 2015 at 12:26:03PM +0000, Mark Rutland wrote:
> On Wed, Jan 07, 2015 at 02:56:51PM +0000, Mark Rutland wrote:
> > When initialising an event, perf_init_event will call try_module_get to
> > ensure that the PMU's module cannot be removed for the lifetime of the
> > event, with __free_event dropping the reference when the event is
> > finally destroyed. If something fails after the event has been
> > initialised, but before the event is installed, perf_event_alloc will
> > drop the reference on the module.
> > 
> > However, if we fail to initialise an event for some reason (e.g. we ask
> > an uncore PMU to perform sampling, and it refuses to initialise the
> > event), we do not drop the refcount. If we try to open such a bogus
> > event without a precise IDR type, we will loop over each PMU in the pmus
> > list, incrementing each of their refcounts without decrementing them.
> > 
> > This patch adds a module_put when pmu->event_init(event) fails, ensuring
> > that the refcounts are balanced in failure cases. As the innards of the
> > precise and search based initialisation look very similar, this logic is
> > hoisted out into a new helper function. While the early return for the
> > failed try_module_get is removed from the search case, this is handled
> > by the remaining return when ret is not -ENOENT.
> 
> I hate to ping, but is anyone going to look at this?
> 

Thanks for reminding me; the inbox is still a horrid mess.

Looks good, thanks!
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