[PATCH 5.15 618/779] perf tools: Fix dso_id inode generation comparison

[Greg Kroah-Hartman]

From: Adrian Hunter <adrian.hunter@xxxxxxxxx>

[ Upstream commit 68566a7cf56bf3148797c218ed45a9de078ef47c ]

Synthesized MMAP events have zero ino_generation, so do not compare
them to DSOs with a real ino_generation otherwise we end up with a DSO
without a build id.

Fixes: 0e3149f86b99ddab ("perf dso: Move dso_id from 'struct map' to 'struct dso'")
Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220711093218.10967-2-adrian.hunter@xxxxxxxxx
[ Added clarification to the comment from Ian + more detailed explanation from Adrian ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/perf/util/dsos.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/dsos.c b/tools/perf/util/dsos.c
index 183a81d5b2f9..2db91121bdaf 100644
--- a/tools/perf/util/dsos.c
+++ b/tools/perf/util/dsos.c
@@ -20,8 +20,19 @@ static int __dso_id__cmp(struct dso_id *a, struct dso_id *b)
 	if (a->ino > b->ino) return -1;
 	if (a->ino < b->ino) return 1;
 
-	if (a->ino_generation > b->ino_generation) return -1;
-	if (a->ino_generation < b->ino_generation) return 1;
+	/*
+	 * Synthesized MMAP events have zero ino_generation, avoid comparing
+	 * them with MMAP events with actual ino_generation.
+	 *
+	 * I found it harmful because the mismatch resulted in a new
+	 * dso that did not have a build ID whereas the original dso did have a
+	 * build ID. The build ID was essential because the object was not found
+	 * otherwise. - Adrian
+	 */
+	if (a->ino_generation && b->ino_generation) {
+		if (a->ino_generation > b->ino_generation) return -1;
+		if (a->ino_generation < b->ino_generation) return 1;
+	}
 
 	return 0;
 }
-- 
2.35.1