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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Fri, 31 Oct 2008 10:38:30 +0000 (UTC)
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Subject: svn commit: r184501 - head/sys/compat/linux
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Author: kib
Date: Fri Oct 31 10:38:30 2008
New Revision: 184501
URL: http://svn.freebsd.org/changeset/base/184501

Log:
  The code in linux_proc_exit() contains a race when multiple linux based
  processes exits at the same time.  The linux_emuldata structure is freed
  but p->p_emuldata is left as a dangling pointer to the just freed memory.
  
  The check for W_EXIT in the loop scanning the child processes isn't safe
  since the state of the child process can change right afterwards. Lock
  the process and check the W_EXIT before delivering signal.
  
  Submitted by:	tegge
  Reviewed by:	davidxu
  MFC after:	1 week

Modified:
  head/sys/compat/linux/linux_emul.c

Modified: head/sys/compat/linux/linux_emul.c
==============================================================================
--- head/sys/compat/linux/linux_emul.c	Fri Oct 31 10:14:28 2008	(r184500)
+++ head/sys/compat/linux/linux_emul.c	Fri Oct 31 10:38:30 2008	(r184501)
@@ -235,11 +235,11 @@ linux_proc_exit(void *arg __unused, stru
 			continue;
 		em = em_find(q, EMUL_DOLOCK);
 		KASSERT(em != NULL, ("linux_reparent: emuldata not found: %i\n", q->p_pid));
-		if (em->pdeath_signal != 0) {
-			PROC_LOCK(q);
+		PROC_LOCK(q);
+		if ((q->p_flag & P_WEXIT) == 0 && em->pdeath_signal != 0) {
 			psignal(q, em->pdeath_signal);
-			PROC_UNLOCK(q);
 		}
+		PROC_UNLOCK(q);
 		EMUL_UNLOCK(&emul_lock);
 	}
 	sx_xunlock(&proctree_lock);