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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 10 Nov 2014 14:11:17 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r274343 - head/sys/kern
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Author: kib
Date: Mon Nov 10 14:11:17 2014
New Revision: 274343
URL: https://svnweb.freebsd.org/changeset/base/274343

Log:
  When sleeping waiting for the profiling stop, always set P_STOPPROF
  before dropping process lock.  Clear P_STOPPROF when doing wakeup.
  
  Both issues caused thread to hang in stopprofclock() "stopprof" sleep.
  
  Reported and tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/kern/kern_clock.c
  head/sys/kern/subr_prof.c

Modified: head/sys/kern/kern_clock.c
==============================================================================
--- head/sys/kern/kern_clock.c	Mon Nov 10 10:59:08 2014	(r274342)
+++ head/sys/kern/kern_clock.c	Mon Nov 10 14:11:17 2014	(r274343)
@@ -668,11 +668,11 @@ stopprofclock(p)
 	PROC_LOCK_ASSERT(p, MA_OWNED);
 	if (p->p_flag & P_PROFIL) {
 		if (p->p_profthreads != 0) {
-			p->p_flag |= P_STOPPROF;
-			while (p->p_profthreads != 0)
+			while (p->p_profthreads != 0) {
+				p->p_flag |= P_STOPPROF;
 				msleep(&p->p_profthreads, &p->p_mtx, PPAUSE,
 				    "stopprof", 0);
-			p->p_flag &= ~P_STOPPROF;
+			}
 		}
 		if ((p->p_flag & P_PROFIL) == 0)
 			return;

Modified: head/sys/kern/subr_prof.c
==============================================================================
--- head/sys/kern/subr_prof.c	Mon Nov 10 10:59:08 2014	(r274342)
+++ head/sys/kern/subr_prof.c	Mon Nov 10 14:11:17 2014	(r274343)
@@ -533,6 +533,7 @@ out:
 	if (--p->p_profthreads == 0) {
 		if (p->p_flag & P_STOPPROF) {
 			wakeup(&p->p_profthreads);
+			p->p_flag &= ~P_STOPPROF;
 			stop = 0;
 		}
 	}