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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Fri, 18 Nov 2011 09:12:26 +0000 (UTC)
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Subject: svn commit: r227657 - in head/sys: kern sys
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Author: kib
Date: Fri Nov 18 09:12:26 2011
New Revision: 227657
URL: http://svn.freebsd.org/changeset/base/227657

Log:
  Consistently use process spin lock for protection of the
  p->p_boundary_count. Race could cause the execve(2) from the threaded
  process to hung since thread boundary counter was incorrect and
  single-threading never finished.
  
  Reported by:	pluknet, pho
  Tested by:	pho
  MFC after:	1 week

Modified:
  head/sys/kern/kern_thread.c
  head/sys/sys/proc.h

Modified: head/sys/kern/kern_thread.c
==============================================================================
--- head/sys/kern/kern_thread.c	Fri Nov 18 09:05:25 2011	(r227656)
+++ head/sys/kern/kern_thread.c	Fri Nov 18 09:12:26 2011	(r227657)
@@ -566,6 +566,8 @@ calc_remaining(struct proc *p, int mode)
 {
 	int remaining;
 
+	PROC_LOCK_ASSERT(p, MA_OWNED);
+	PROC_SLOCK_ASSERT(p, MA_OWNED);
 	if (mode == SINGLE_EXIT)
 		remaining = p->p_numthreads;
 	else if (mode == SINGLE_BOUNDARY)
@@ -819,8 +821,11 @@ thread_suspend_check(int return_instead)
 			td->td_flags &= ~TDF_BOUNDARY;
 		thread_unlock(td);
 		PROC_LOCK(p);
-		if (return_instead == 0)
+		if (return_instead == 0) {
+			PROC_SLOCK(p);
 			p->p_boundary_count--;
+			PROC_SUNLOCK(p);
+		}
 	}
 	return (0);
 }

Modified: head/sys/sys/proc.h
==============================================================================
--- head/sys/sys/proc.h	Fri Nov 18 09:05:25 2011	(r227656)
+++ head/sys/sys/proc.h	Fri Nov 18 09:12:26 2011	(r227657)
@@ -532,7 +532,7 @@ struct proc {
 	struct thread	*p_singlethread;/* (c + j) If single threading this is it */
 	int		p_suspcount;	/* (j) Num threads in suspended mode. */
 	struct thread	*p_xthread;	/* (c) Trap thread */
-	int		p_boundary_count;/* (c) Num threads at user boundary */
+	int		p_boundary_count;/* (j) Num threads at user boundary */
 	int		p_pendingcnt;	/* how many signals are pending */
 	struct itimers	*p_itimers;	/* (c) POSIX interval timers. */
 	struct procdesc	*p_procdesc;	/* (e) Process descriptor, if any. */