From owner-cvs-all@FreeBSD.ORG  Wed Mar  2 22:55:41 2005
Return-Path: <owner-cvs-all@FreeBSD.ORG>
Delivered-To: cvs-all@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 9682616A4CE; Wed,  2 Mar 2005 22:55:41 +0000 (GMT)
Received: from freefall.freebsd.org (freefall.freebsd.org [216.136.204.21])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 75A5643D31; Wed,  2 Mar 2005 22:55:41 +0000 (GMT)
	(envelope-from davidxu@freebsd.org)
Received: from [127.0.0.1] (davidxu@localhost [127.0.0.1])
	by freefall.freebsd.org (8.13.1/8.13.1) with ESMTP id j22MtdFS034152;
	Wed, 2 Mar 2005 22:55:40 GMT
	(envelope-from davidxu@freebsd.org)
Message-ID: <4226446B.7020406@freebsd.org>
Date: Thu, 03 Mar 2005 06:55:39 +0800
From: David Xu <davidxu@freebsd.org>
User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US;
	rv:1.7.2) Gecko/20041004
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: John Baldwin <jhb@freebsd.org>
References: <200503021343.j22DhpQ3075008@repoman.freebsd.org>
	<200503020915.28512.jhb@FreeBSD.org>
In-Reply-To: <200503020915.28512.jhb@FreeBSD.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
cc: cvs-src@freebsd.org
cc: src-committers@freebsd.org
cc: cvs-all@freebsd.org
Subject: Re: cvs commit: src/sys/kern kern_sig.c
X-BeenThere: cvs-all@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: CVS commit messages for the entire tree <cvs-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-all>,
	<mailto:cvs-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/cvs-all>
List-Post: <mailto:cvs-all@freebsd.org>
List-Help: <mailto:cvs-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-all>,
	<mailto:cvs-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 02 Mar 2005 22:55:41 -0000

John Baldwin wrote:

>On Wednesday 02 March 2005 08:43 am, David Xu wrote:
>  
>
>>davidxu     2005-03-02 13:43:51 UTC
>>
>>  FreeBSD src repository
>>
>>  Modified files:
>>    sys/kern             kern_sig.c
>>  Log:
>>  In kern_sigtimedwait, remove waitset bits for td_sigmask before
>>  sleeping, so in do_tdsignal, we no longer need to test td_waitset.
>>  now td_waitset is only used to give a thread higher priority when
>>  delivering signal to multithreads process.
>>  This also fixes a bug:
>>  when a thread in sigwait states was suspended and later resumed
>>  by SIGCONT, it can no longer receive signals belong to waitset.
>>    
>>
>
>Is this related at all to Peter Holm's panic where sigwait() + swapping 
>invokes a panic?
>
>  
>
No. Peter Holm's found is a swapping problem. vm swaps out sleeping
thread's stack under memory stressing case. but I think that's not safe,
that means, following code can not be used in kernel:

int *p;

func()
 {
    int n;

    n = 0;
    p = &n;
    msleep(p);
    /* check variable n ...
}

func2()
{
   *p = 2;
   wakeup(p);
}

unless million lines of kernel code are reviewed, I don't think the
vm code is safe. The following patch should avoid the problem:

Index: vm_glue.c
===================================================================
RCS file: /home/ncvs/src/sys/vm/vm_glue.c,v
retrieving revision 1.210
diff -u -r1.210 vm_glue.c
--- vm_glue.c    22 Jan 2005 19:21:29 -0000    1.210
+++ vm_glue.c    2 Mar 2005 11:22:32 -0000
@@ -334,6 +334,7 @@
 void
 vm_thread_swapout(struct thread *td)
 {
+#if 0
     vm_object_t ksobj;
     vm_page_t m;
     int i, pages;
@@ -353,6 +354,7 @@
         vm_page_unlock_queues();
     }
     VM_OBJECT_UNLOCK(ksobj);
+#endif
 }
 
 /*

---
David Xu