linux-kernel - Re: [BUG PATCH] perf: kvm - finding struct machine fails for PERF_RECORD

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Date:	Mon, 09 Apr 2012 16:59:50 -0600
From:	David Ahern <dsahern@...il.com>
To:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
CC:	mingo@...hat.com, acme@...stprotocols.net, a.p.zijlstra@...llo.nl,
	paulus@...ba.org, fweisbec@...il.com, eranian@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG PATCH] perf: kvm - finding struct machine fails for PERF_RECORD_MMAP

On 4/9/12 2:22 AM, Nikunj A. Dadhania wrote:
> From: Nikunj A. Dadhania<nikunj@...ux.vnet.ibm.com>
>
> Running 'perf kvm --host --guest --guestmount /tmp/guestmount record -a -g -- sleep 2'
>
> Was resulting in a segfault. For event type PERF_RECORD_MMAP,
> event->ip.pid is being used in perf_session__find_machine_for_cpumode,
> which is not correct.
>
> event->ip.pid happens to be 0 in this case and results in returning a
> NULL machine object. Finally, access to self->pid in
> machine__mmap_name, results in a segfault later.

I have tried unsuccessfully to recreate the segfault. All of the samples 
I get are of type PERF_RECORD_SAMPLE. I do not see how an MMAP event can 
be generated in a guest context.

David


>
> For PERF_RECORD_MMAP type, pass event->mmap.pid.
>
> Signed-off-by: Nikunj A. Dadhania<nikunj@...ux.vnet.ibm.com>
> ---
>
>   tools/perf/util/session.c |   12 ++++++++++--
>   1 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 9412e3b..00923cd 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -826,8 +826,16 @@ static struct machine *
>   {
>   	const u8 cpumode = event->header.misc&  PERF_RECORD_MISC_CPUMODE_MASK;
>
> -	if (cpumode == PERF_RECORD_MISC_GUEST_KERNEL&&  perf_guest)
> -		return perf_session__find_machine(session, event->ip.pid);
> +	if (cpumode == PERF_RECORD_MISC_GUEST_KERNEL&&  perf_guest) {
> +		u32 pid;
> +
> +		if (event->header.type == PERF_RECORD_MMAP)
> +			pid = event->mmap.pid;
> +		else
> +			pid = event->ip.pid;
> +
> +		return perf_session__find_machine(session, pid);
> +	}
>
>   	return perf_session__find_host_machine(session);
>   }
>
> --
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