From owner-svn-src-all@FreeBSD.ORG  Sat Sep 22 12:17:09 2012
Return-Path: <owner-svn-src-all@FreeBSD.ORG>
Delivered-To: svn-src-all@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
	by hub.freebsd.org (Postfix) with ESMTP id CFD20106564A;
	Sat, 22 Sep 2012 12:17:09 +0000 (UTC) (envelope-from kib@FreeBSD.org)
Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:4f8:fff6::2c])
	by mx1.freebsd.org (Postfix) with ESMTP id BC4108FC15;
	Sat, 22 Sep 2012 12:17:09 +0000 (UTC)
Received: from svn.freebsd.org (localhost [127.0.0.1])
	by svn.freebsd.org (8.14.4/8.14.4) with ESMTP id q8MCH9ob064473;
	Sat, 22 Sep 2012 12:17:09 GMT (envelope-from kib@svn.freebsd.org)
Received: (from kib@localhost)
	by svn.freebsd.org (8.14.4/8.14.4/Submit) id q8MCH9Ip064471;
	Sat, 22 Sep 2012 12:17:09 GMT (envelope-from kib@svn.freebsd.org)
Message-Id: <201209221217.q8MCH9Ip064471@svn.freebsd.org>
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 22 Sep 2012 12:17:09 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
	svn-src-head@freebsd.org
X-SVN-Group: head
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Cc: 
Subject: svn commit: r240813 - head/sys/kern
X-BeenThere: svn-src-all@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: "SVN commit messages for the entire src tree \(except for &quot;
	user&quot; and &quot; projects&quot; \)" <svn-src-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
	<mailto:svn-src-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/svn-src-all>
List-Post: <mailto:svn-src-all@freebsd.org>
List-Help: <mailto:svn-src-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/svn-src-all>,
	<mailto:svn-src-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 22 Sep 2012 12:17:09 -0000

Author: kib
Date: Sat Sep 22 12:17:09 2012
New Revision: 240813
URL: http://svn.freebsd.org/changeset/base/240813

Log:
  Do not skip two elements of the tid_buffer when reusing the buffer
  slot. This eventually results in exhaustion of the tid space, causing
  new threads get tid -1 as identifier.
  
  The bad effect of having the thread id equal to -1 is that
  UMTX_OP_UMUTEX_WAIT returns EFAULT for a lock owned by such thread,
  because casuword cannot distinguish between literal value -1 read from
  the address and -1 returned as an indication of faulted
  access. _thr_umutex_lock() helper from libthr does not check for
  errors from _umtx_op_err(2), causing an infinite loop in
  mutex_lock_sleep().
  
  We observed the JVM processes hanging and consuming enormous amount of
  system time on machines with approximately 100 days uptime.
  
  Reported by:	Mykola Dzham <freebsd levsha org ua>
  MFC after:	1 week

Modified:
  head/sys/kern/kern_thread.c

Modified: head/sys/kern/kern_thread.c
==============================================================================
--- head/sys/kern/kern_thread.c	Sat Sep 22 12:12:39 2012	(r240812)
+++ head/sys/kern/kern_thread.c	Sat Sep 22 12:17:09 2012	(r240813)
@@ -116,7 +116,7 @@ tid_free(lwpid_t tid)
 	mtx_lock(&tid_lock);
 	if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
 		tmp_tid = tid_buffer[tid_head++];
-		tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
+		tid_head %= TID_BUFFER_SIZE;
 	}
 	tid_buffer[tid_tail++] = tid;
 	tid_tail %= TID_BUFFER_SIZE;