Re: [BUG PATCH] perf: kvm - finding struct machine fails for PERF_RECORD_MMAP

From: David Ahern
Date: Mon Apr 09 2012 - 18:59:51 EST


On 4/9/12 2:22 AM, Nikunj A. Dadhania wrote:
From: Nikunj A. Dadhania<nikunj@xxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxx>
---

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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