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

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Message-ID: <20120409081835.10576.22018.stgit@abhimanyu.in.ibm.com>
Date:	Mon, 09 Apr 2012 13:52:23 +0530
From:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
To:	mingo@...hat.com, acme@...stprotocols.net, dsahern@...il.com
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org, fweisbec@...il.com,
	eranian@...gle.com, linux-kernel@...r.kernel.org,
	nikunj@...ux.vnet.ibm.com
Subject: [BUG PATCH] perf: kvm - finding struct machine fails for
 PERF_RECORD_MMAP

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.

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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