pid allocator bug ?

pid allocator bug ?

[J.A. Magallon]

On 20020215 Erik Arjan Hendriks wrote:
>BProc 3.1.7 is out and in the usual spot:
>
>http://sourceforge.net/project/showfiles.php?group_id=24453&release_id=75172
>
>Release notes and change log follow:
>
...
>
>        * Added patch for Linux PID allocator bug.
>

Patch is like this:

$Id: linux-2.4.17-fork-pid-alloc.patch,v 1.1 2002/02/14 17:21:35 hendriks Exp $

This patch fixes a bug in the Linux process ID allocator.  It isn't quite
SMP safe since it references "last_pid" after releasing the lock protecting
it.  This can result in two processes getting assigned the same process ID.

--- linux-2.4.17/kernel/fork.c.orig	Mon Feb  4 14:53:31 2002
+++ linux-2.4.17/kernel/fork.c	Mon Feb  4 14:53:53 2002
@@ -85,6 +85,7 @@
 {
 	static int next_safe = PID_MAX;
 	struct task_struct *p;
+	int pid;
 
 	if (flags & CLONE_PID)
 		return current->pid;
@@ -120,9 +121,10 @@
 		}
 		read_unlock(&tasklist_lock);
 	}
+	pid = last_pid;
 	spin_unlock(&lastpid_lock);
 
-	return last_pid;
+	return pid;
 }
 
 static inline int dup_mmap(struct mm_struct * mm)

????

-- 
J.A. Magallon                           #  Let the source be with you...        
mailto:jamagallon@able.es
Mandrake Linux release 8.2 (Cooker) for i586
Linux werewolf 2.4.18-rc1-slb1 #1 SMP Thu Feb 14 01:04:12 CET 2002 i686