linux-kernel - [PATCH v3 07/27] core: optimize setrlimit for current task

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Message-Id: <1259363167-9347-7-git-send-email-jslaby@suse.cz>
Date:	Sat, 28 Nov 2009 00:05:47 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	jirislaby@...il.com
Cc:	mingo@...e.hu, nhorman@...driver.com, sfr@...b.auug.org.au,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	marcin.slusarz@...il.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, torvalds@...ux-foundation.org, oleg@...hat.com
Subject: [PATCH v3 07/27] core: optimize setrlimit for current task

From: Jiri Slaby <jirislaby@...il.com>

Don't take tasklist lock for 'current'. It's not needed, since
current->sighand/signal can't disappear.

This improves serlimit called especially via sys_setrlimit.

Signed-off-by: Jiri Slaby <jirislaby@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>
---
 kernel/sys.c |   16 ++++++++++------
 1 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 3082eaf..605ab9c 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1250,11 +1250,14 @@ int setrlimit(struct task_struct *tsk, unsigned int resource,
 	if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
 		return -EPERM;
 
-	/* protect tsk->signal and tsk->sighand from disappearing */
-	read_lock(&tasklist_lock);
-	if (!tsk->sighand) {
-		retval = -ESRCH;
-		goto out;
+	/* optimization: 'current' doesn't need locking, e.g. setrlimit */
+	if (tsk != current) {
+		/* protect tsk->signal and tsk->sighand from disappearing */
+		read_lock(&tasklist_lock);
+		if (!tsk->sighand) {
+			retval = -ESRCH;
+			goto out;
+		}
 	}
 
 	retval = security_task_setrlimit(tsk, resource, new_rlim);
@@ -1294,7 +1297,8 @@ int setrlimit(struct task_struct *tsk, unsigned int resource,
 
 	update_rlimit_cpu(tsk, new_rlim->rlim_cur);
 out:
-	read_unlock(&tasklist_lock);
+	if (tsk != current)
+		read_unlock(&tasklist_lock);
 	return retval;
 }
 
-- 
1.6.5.3

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