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SubjectRe: [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) {
/*
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