linux-kernel - [PATCH] umh: Optimize 'proc_cap

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Date:   Fri, 20 Oct 2017 21:33:31 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     mcgrof@...nel.org
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] umh: Optimize 'proc_cap_handler()'

If 'write' is 0, we can avoid a call to spin_lock/spin_unlock.

Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
 kernel/umh.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/umh.c b/kernel/umh.c
index 6ff9905250ff..18e5fa4b0e71 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -537,14 +537,14 @@ static int proc_cap_handler(struct ctl_table *table, int write,
 	/*
 	 * Drop everything not in the new_cap (but don't add things)
 	 */
-	spin_lock(&umh_sysctl_lock);
 	if (write) {
+		spin_lock(&umh_sysctl_lock);
 		if (table->data == CAP_BSET)
 			usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap);
 		if (table->data == CAP_PI)
 			usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap);
+		spin_unlock(&umh_sysctl_lock);
 	}
-	spin_unlock(&umh_sysctl_lock);
 
 	return 0;
 }
-- 
2.14.1