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Date:      Fri, 13 Sep 2013 06:39:11 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r255509 - head/sys/kern
Message-ID:  <201309130639.r8D6dBnC053663@svn.freebsd.org>
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Author: kib
Date: Fri Sep 13 06:39:10 2013
New Revision: 255509
URL: http://svnweb.freebsd.org/changeset/base/255509

Log:
  Reduce the scope of the proctree_lock. If several processes cause
  continuous calls to the uprintf(9), the proctree_lock could be
  shared-locked for indefinite amount of time, starving exclusive
  requests. Since proctree_lock is needed for fork() and exit(), this
  effectively stops the machine.
  
  While there, do the similar reduction for tprintf(9).
  
  Reported and tested by: pho
  Reviewed by:    ed
  Sponsored by:   The FreeBSD Foundation
  MFC after:	1 week
  Approved by:	re (glebius)

Modified:
  head/sys/kern/subr_prf.c

Modified: head/sys/kern/subr_prf.c
==============================================================================
--- head/sys/kern/subr_prf.c	Fri Sep 13 06:18:33 2013	(r255508)
+++ head/sys/kern/subr_prf.c	Fri Sep 13 06:39:10 2013	(r255509)
@@ -151,26 +151,25 @@ uprintf(const char *fmt, ...)
 	PROC_LOCK(p);
 	if ((p->p_flag & P_CONTROLT) == 0) {
 		PROC_UNLOCK(p);
-		retval = 0;
-		goto out;
+		sx_sunlock(&proctree_lock);
+		return (0);
 	}
 	SESS_LOCK(p->p_session);
 	pca.tty = p->p_session->s_ttyp;
 	SESS_UNLOCK(p->p_session);
 	PROC_UNLOCK(p);
 	if (pca.tty == NULL) {
-		retval = 0;
-		goto out;
+		sx_sunlock(&proctree_lock);
+		return (0);
 	}
 	pca.flags = TOTTY;
 	pca.p_bufr = NULL;
 	va_start(ap, fmt);
 	tty_lock(pca.tty);
+	sx_sunlock(&proctree_lock);
 	retval = kvprintf(fmt, putchar, &pca, 10, ap);
 	tty_unlock(pca.tty);
 	va_end(ap);
-out:
-	sx_sunlock(&proctree_lock);
 	return (retval);
 }
 
@@ -219,13 +218,13 @@ vtprintf(struct proc *p, int pri, const 
 	pca.p_bufr = NULL;
 	if (pca.tty != NULL)
 		tty_lock(pca.tty);
+	sx_sunlock(&proctree_lock);
 	kvprintf(fmt, putchar, &pca, 10, ap);
 	if (pca.tty != NULL)
 		tty_unlock(pca.tty);
 	if (sess != NULL)
 		sess_release(sess);
 	msgbuftrigger = 1;
-	sx_sunlock(&proctree_lock);
 }
 
 /*

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