linux-kernel - [RFC,PATCH 2/2] kill_pid_info: don't take now unneeded tasklist

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Message-ID: <20080304185745.GA8482@tv-sign.ru>
Date:	Tue, 4 Mar 2008 21:57:45 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Ingo Molnar <mingo@...e.hu>, Jiri Kosina <jkosina@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	linux-kernel@...r.kernel.org
Subject: [RFC,PATCH 2/2] kill_pid_info: don't take now unneeded tasklist_lock

Previously handle_stop_signal(SIGCONT) could drop ->siglock. That is why
kill_pid_info(SIGCONT) takes tasklist_lock to make sure the target task
can't go away after unlock. Not needed now.

Signed-off-by: Oleg Nesterov <oleg@...sign.ru>

--- 25/include/linux/signal.h~1__KILL_NO_TASKLIST	2008-02-15 16:59:17.000000000 +0300
+++ 25/include/linux/signal.h	2008-03-04 21:43:25.000000000 +0300
@@ -362,8 +362,6 @@ int unhandled_signal(struct task_struct 
 #define sig_kernel_stop(sig) \
 	(((sig) < SIGRTMIN) && siginmask(sig, SIG_KERNEL_STOP_MASK))
 
-#define sig_needs_tasklist(sig)	((sig) == SIGCONT)
-
 #define sig_user_defined(t, signr) \
 	(((t)->sighand->action[(signr)-1].sa.sa_handler != SIG_DFL) &&	\
 	 ((t)->sighand->action[(signr)-1].sa.sa_handler != SIG_IGN))
--- 25/kernel/signal.c~1__KILL_NO_TASKLIST	2008-03-04 21:24:20.000000000 +0300
+++ 25/kernel/signal.c	2008-03-04 21:44:58.000000000 +0300
@@ -1030,9 +1030,6 @@ int kill_pid_info(int sig, struct siginf
 	struct task_struct *p;
 
 	rcu_read_lock();
-	if (unlikely(sig_needs_tasklist(sig)))
-		read_lock(&tasklist_lock);
-
 retry:
 	p = pid_task(pid, PIDTYPE_PID);
 	if (p) {
@@ -1046,10 +1043,8 @@ retry:
 			 */
 			goto retry;
 	}
-
-	if (unlikely(sig_needs_tasklist(sig)))
-		read_unlock(&tasklist_lock);
 	rcu_read_unlock();
+
 	return error;
 }
 

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