linux-kernel - [PATCH] perf kcore_copy: Do not check /proc/modules is unchanged

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Date:   Wed, 14 Sep 2022 15:24:29 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Daniel Dao <dqminh@...udflare.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: [PATCH] perf kcore_copy: Do not check /proc/modules is unchanged

/proc/kallsyms and /proc/modules are compared before and after the copy
in order to ensure no changes during the copy. However /proc/modules
also might change due to reference counts changing even though that
does not make any difference. Any modules loaded or unloaded should be
visible in changes to kallsyms, so it is not necessary to check
/proc/modules also anyway.

Remove the comparison checking that /proc/modules is unchanged.

Reported-by: Daniel Dao <dqminh@...udflare.com>
Fixes: fc1b691d7651 ("perf buildid-cache: Add ability to add kcore to the cache")
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/perf/util/symbol-elf.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 75bec32d4f57..647b7dff8ef3 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -2102,8 +2102,8 @@ static int kcore_copy__compare_file(const char *from_dir, const char *to_dir,
  * unusual.  One significant peculiarity is that the mapping (start -> pgoff)
  * is not the same for the kernel map and the modules map.  That happens because
  * the data is copied adjacently whereas the original kcore has gaps.  Finally,
- * kallsyms and modules files are compared with their copies to check that
- * modules have not been loaded or unloaded while the copies were taking place.
+ * kallsyms file is compared with its copy to check that modules have not been
+ * loaded or unloaded while the copies were taking place.
  *
  * Return: %0 on success, %-1 on failure.
  */
@@ -2166,9 +2166,6 @@ int kcore_copy(const char *from_dir, const char *to_dir)
 			goto out_extract_close;
 	}
 
-	if (kcore_copy__compare_file(from_dir, to_dir, "modules"))
-		goto out_extract_close;
-
 	if (kcore_copy__compare_file(from_dir, to_dir, "kallsyms"))
 		goto out_extract_close;
 
-- 
2.25.1