linux-kernel - [PATCH] selftests: mm: restore settings from only parent process

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Date: Thu, 14 Mar 2024 14:40:45 +0500
From: Muhammad Usama Anjum <usama.anjum@...labora.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	Shuah Khan <shuah@...nel.org>,
	Muhammad Usama Anjum <usama.anjum@...labora.com>
Cc: kernel@...labora.com,
	Joey Gouly <joey.gouly@....com>,
	linux-mm@...ck.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] selftests: mm: restore settings from only parent process

The atexit() is called from parent process as well as forked processes.
Hence the child restores the settings at exit while the parent is still
executing. Fix this by checking pid of atexit() calling process and only
restore THP number from parent process.

Fixes: c23ea61726d5 ("selftests/mm: protection_keys: save/restore nr_hugepages settings")
Tested-by: Joey Gouly <joey.gouly@....com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
---
 tools/testing/selftests/mm/protection_keys.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
index f822ae31af22e..374a308174d2b 100644
--- a/tools/testing/selftests/mm/protection_keys.c
+++ b/tools/testing/selftests/mm/protection_keys.c
@@ -1745,9 +1745,12 @@ void pkey_setup_shadow(void)
 	shadow_pkey_reg = __read_pkey_reg();
 }
 
+pid_t parent_pid;
+
 void restore_settings_atexit(void)
 {
-	cat_into_file(buf, "/proc/sys/vm/nr_hugepages");
+	if (parent_pid == getpid())
+		cat_into_file(buf, "/proc/sys/vm/nr_hugepages");
 }
 
 void save_settings(void)
@@ -1773,6 +1776,7 @@ void save_settings(void)
 		exit(__LINE__);
 	}
 
+	parent_pid = getpid();
 	atexit(restore_settings_atexit);
 	close(fd);
 }
-- 
2.39.2