From d54c730eba63dfe0dcb8c7ab41514c564c159212 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jirislaby@gmail.com>
Date: Fri, 28 Aug 2009 14:08:17 +0200
Subject: [PATCH] core: optimize setrlimit for current task
References: FATE#305733
Patch-mainline: no (later)

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 <jslaby@suse.cz>
Cc: Oleg Nesterov <oleg@redhat.com>
---
 kernel/sys.c |   16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1316,11 +1316,14 @@ int do_setrlimit(struct task_struct *tsk
 	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);
@@ -1360,7 +1363,8 @@ int do_setrlimit(struct task_struct *tsk
 
 	update_rlimit_cpu(tsk, new_rlim->rlim_cur);
 out:
-	read_unlock(&tasklist_lock);
+	if (tsk != current)
+		read_unlock(&tasklist_lock);
 	return retval;
 }
 
