linux-kernel - Re: [PATCH 2/2] perf report: Don't add to histogram when there is no thread found

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Date:   Mon, 26 Jun 2023 17:02:27 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     James Clark <james.clark@....com>, Ian Rogers <irogers@...gle.com>
Cc:     linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] perf report: Don't add to histogram when there is no
 thread found

On Mon, Jun 26, 2023 at 05:10:58PM +0100, James Clark wrote:
> thread__find_map() chooses to exit without assigning a thread to the
> addr_location in some scenarios, for example when there are samples from
> a guest and perf_guest == false. This results in a segfault when adding
> to the histogram because it uses unguarded accesses to the thread member
> of the addr_location.

Looking at the commit 0dd5041c9a0ea ("perf addr_location: Add
init/exit/copy functions") that introduced the change, I'm not sure if
it's the intend behavior.

It might change maps and map, but not thread.  Then I think no reason
to not set the al->thread at the beginning.

How about this?  Ian?
(I guess we can get rid of the duplicate 'al->map = NULL' part)

Thanks,
Namhyung


---8<---
 
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 3860b0c74829..4cbb092e0684 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -581,15 +581,14 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr,
 	maps__zput(al->maps);
 	map__zput(al->map);
 	thread__zput(al->thread);
+	al->thread = thread__get(thread);
 
 	al->addr = addr;
 	al->cpumode = cpumode;
 	al->filtered = 0;
 
-	if (machine == NULL) {
-		al->map = NULL;
+	if (machine == NULL)
 		return NULL;
-	}
 
 	if (cpumode == PERF_RECORD_MISC_KERNEL && perf_host) {
 		al->level = 'k';
@@ -605,7 +604,6 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr,
 		al->level = 'u';
 	} else {
 		al->level = 'H';
-		al->map = NULL;
 
 		if ((cpumode == PERF_RECORD_MISC_GUEST_USER ||
 			cpumode == PERF_RECORD_MISC_GUEST_KERNEL) &&
@@ -619,7 +617,6 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr,
 		return NULL;
 	}
 	al->maps = maps__get(maps);
-	al->thread = thread__get(thread);
 	al->map = map__get(maps__find(maps, al->addr));
 	if (al->map != NULL) {
 		/*