linux-kernel - [PATCH 2/2] uglify while_each_pid_task() to make sure we don't count the execing pricess twice

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Date:	Fri, 7 Dec 2007 20:03:34 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] uglify while_each_pid_task() to make sure we don't count the execing pricess twice

There is a window when de_thread() switches the leader and drops tasklist_lock.
In that window do_each_pid_task(PIDTYPE_PID) finds both new and old leaders.

The problem is pretty much theoretical and probably can be ignored. Currently
the only users of do_each_pid_task(PIDTYPE_PID) are send_sigio/send_sigurg, so
they can send the signal to the same process twice.

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

--- PT/include/linux/pid.h~2_do_each_pid_task	2007-10-25 16:22:12.000000000 +0400
+++ PT/include/linux/pid.h	2007-12-07 18:24:21.000000000 +0300
@@ -160,7 +160,13 @@ static inline pid_t pid_vnr(struct pid *
 			hlist_for_each_entry_rcu((task), pos___,	\
 				&pid->tasks[type], pids[type].node) {
 
+			/*
+			 * Both old and new leaders may be attached to
+			 * the same pid in the middle of de_thread().
+			 */
 #define while_each_pid_task(pid, type, task)				\
+				if (type == PIDTYPE_PID)		\
+					break;				\
 			}						\
 	} while (0)
 

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