From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mark Fasheh <mfasheh@suse.de>
Date: Fri, 19 Dec 2014 12:25:03 -0800
Subject: [Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address
	when read	o2dlm debug messages
In-Reply-To: <5493E31F.2000509@huawei.com>
References: <548f65d4.jhly8vWOTpWuHPjg%akpm@linux-foundation.org>
	<20141216222629.GO7238@wotan.suse.de> <5493E31F.2000509@huawei.com>
Message-ID: <20141219202503.GX7238@wotan.suse.de>
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To: ocfs2-devel@oss.oracle.com

On Fri, Dec 19, 2014 at 04:34:39PM +0800, jiangyiwen wrote:
> ? 2014/12/17 6:26, Mark Fasheh ??:
> > On Mon, Dec 15, 2014 at 02:51:00PM -0800, Andrew Morton wrote:
> >> In such a race case, invalid address access may occurs.  So we should
> >> delete list res->tracking before resA->refs decrease to 0.
> >>
> > 
> > 
> >> diff -puN fs/ocfs2/dlm/dlmmaster.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages fs/ocfs2/dlm/dlmmaster.c
> >> --- a/fs/ocfs2/dlm/dlmmaster.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages
> >> +++ a/fs/ocfs2/dlm/dlmmaster.c
> >> @@ -498,16 +498,6 @@ static void dlm_lockres_release(struct k
> >>  	mlog(0, "destroying lockres %.*s\n", res->lockname.len,
> >>  	     res->lockname.name);
> >>  
> >> -	spin_lock(&dlm->track_lock);
> >> -	if (!list_empty(&res->tracking))
> >> -		list_del_init(&res->tracking);
> >> -	else {
> >> -		mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
> >> -		     res->lockname.len, res->lockname.name);
> >> -		dlm_print_one_lock_resource(res);
> >> -	}
> >> -	spin_unlock(&dlm->track_lock);
> >> -
> >>  	atomic_dec(&dlm->res_cur_count);
> >>  
> >>  	if (!hlist_unhashed(&res->hash_node) ||
> >> diff -puN fs/ocfs2/dlm/dlmthread.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages fs/ocfs2/dlm/dlmthread.c
> >> --- a/fs/ocfs2/dlm/dlmthread.c~ocfs2-avoid-access-invalid-address-when-read-o2dlm-debug-messages
> >> +++ a/fs/ocfs2/dlm/dlmthread.c
> >> @@ -211,6 +211,16 @@ static void dlm_purge_lockres(struct dlm
> >>  
> >>  	__dlm_unhash_lockres(dlm, res);
> >>  
> >> +	spin_lock(&dlm->track_lock);
> >> +	if (!list_empty(&res->tracking))
> >> +		list_del_init(&res->tracking);
> >> +	else {
> >> +		mlog(ML_ERROR, "Resource %.*s not on the Tracking list\n",
> >> +				res->lockname.len, res->lockname.name);
> >> +		__dlm_print_one_lock_resource(res);
> >> +	}
> >> +	spin_unlock(&dlm->track_lock);
> >> +
> >>  	/* lockres is not in the hash now.  drop the flag and wake up
> >>  	 * any processes waiting in dlm_get_lock_resource. */
> >>  	if (!master) {
> >> _
> > 
> > How do we know that dlm_purge_lockres() is the last caller of
> > dlm_lockres_put()? Don't we now have a problem where if the last ref is
> > dropped by any other function than dlm_purge_lockres() the lockres is freed
> > while on the tracking list?
> > 	--Mark
> > 
> > --
> > Mark Fasheh
> > 
> > .
> > 
> dlm_purge_lockres is not necessarily the last caller of
> dlm_lockres_put(), but it means lockres will be purged if
> dlm_purge_lockres is called. Besides, lockres is also unhashed in
> dlm_purge_lockres, so lockres can be removed from tracking list.
> contents of dlm->tracking_list will be consistent with
> dlm->lockres_hash.

I'm still confused. This is what I'm worried about:

1) a procss calls dlm_lockres_put(), NOT from dlm_purge_lockres().

2) if the count goes to zero, then that process will call dlm_lockres_release()

3) dlm_lockres_release() will free the lockres without removing it from the
tracking list. Thus we will have a corrupted list.

Does that make sense? Am I wrong here?
	--Mark

--
Mark Fasheh