linux-kernel - [PATCH 4.14 33/40] perf kcore_copy: Do not check /proc/modules is unchanged

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Date:   Mon, 26 Sep 2022 12:12:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Daniel Dao <dqminh@...udflare.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 33/40] perf kcore_copy: Do not check /proc/modules is unchanged

From: Adrian Hunter <adrian.hunter@...el.com>

[ Upstream commit 5b427df27b94aec1312cace48a746782a0925c53 ]

/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.

Fixes: fc1b691d7651d949 ("perf buildid-cache: Add ability to add kcore to the cache")
Reported-by: Daniel Dao <dqminh@...udflare.com>
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
Tested-by: Daniel Dao <dqminh@...udflare.com>
Acked-by: Namhyung Kim <namhyung@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Link: https://lore.kernel.org/r/20220914122429.8770-1-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 a0a4afa7e678..866a61d66251 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -1693,8 +1693,8 @@ 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.
  */
@@ -1757,9 +1757,6 @@ int kcore_copy(const char *from_dir, const char *to_dir)
 					 kci.modules_map.len))
 		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;
 
-- 
2.35.1