[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[akpm at linux-foundation.org]

From: jiangyiwen <jiangyiwen@huawei.com>
Subject: ocfs2: avoid access invalid address when read o2dlm debug messages

The following case will lead to a lockres is freed but is still in use.

cat /sys/kernel/debug/o2dlm/locking_state	dlm_thread
lockres_seq_start
    -> lock dlm->track_lock
    -> get resA
                                                resA->refs decrease to 0,
                                                call dlm_lockres_release,
                                                and wait for "cat" unlock.
Although resA->refs is already set to 0,
increase resA->refs, and then unlock
                                                lock dlm->track_lock
                                                    -> list_del_init()
                                                    -> unlock
                                                    -> free resA

In such a race case, invalid address access may occurs.  So we should
delete list res->tracking before resA->refs decrease to 0.


Signed-off-by: jiangyiwen <jiangyiwen@huawei.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/ocfs2/dlm/dlmmaster.c |   10 ----------
 fs/ocfs2/dlm/dlmthread.c |   10 ++++++++++
 2 files changed, 10 insertions(+), 10 deletions(-)

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) {
_

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[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

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[jiangyiwen]

? 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.
	--YiWen Jiang

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[Mark Fasheh]

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

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[jiangyiwen]

? 2014/12/20 4:25, Mark Fasheh ??:
> 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()
> 
But at this time, it has already called dlm_purge_lockres(). The reasons are as follows:
1) lockres is created in dlm_init_lockres(), it call kref_init(), count is 1;
2) Only when lockres is unused, it will call dlm_lockres_put() twice by dlm_run_purge_list().
So dlm_purge_lockres() has been called if the count goes to zero.

> 3) dlm_lockres_release() will free the lockres without removing it from the
> tracking list. Thus we will have a corrupted list.
>
Without this scene. dlm_purge_lockres() is called before dlm_lockres_release().
> Does that make sense? Am I wrong here?
> 	--Mark
> 
> --
> Mark Fasheh
> 
> .
> 

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[Xue jiufei]

Hi jiangyiwen,
On 2014/12/20 17:39, jiangyiwen wrote:
> ? 2014/12/20 4:25, Mark Fasheh ??:
>> 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()
>>
> But at this time, it has already called dlm_purge_lockres(). The reasons are as follows:
> 1) lockres is created in dlm_init_lockres(), it call kref_init(), count is 1;
> 2) Only when lockres is unused, it will call dlm_lockres_put() twice by dlm_run_purge_list().
> So dlm_purge_lockres() has been called if the count goes to zero.
> 
>> 3) dlm_lockres_release() will free the lockres without removing it from the
>> tracking list. Thus we will have a corrupted list.
>>
> Without this scene. dlm_purge_lockres() is called before dlm_lockres_release().
Once lock resource is inserted into hash list, it should call
dlm_purge_lockres()->__dlm_unhash_lockres() to put the last ref.
However, if lock resource is initialized and inserted into tracking
list but not inserted into hash list, it can happen that
dlm_lockres_release() will free the lockres without removing it from
the tracking list.
So we should remove lockres from tracking list if we call
dlm_lockres_put() after lockres is created but not inserted into hash
list yet.

Thanks,
Xuejiufei
>> Does that make sense? Am I wrong here?
>> 	--Mark
>>
>> --
>> Mark Fasheh
>>
>> .
>>
> 
> 
> 
> _______________________________________________
> Ocfs2-devel mailing list
> Ocfs2-devel at oss.oracle.com
> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
> 

[Ocfs2-devel] [patch 04/15] ocfs2: avoid access invalid address when read o2dlm debug messages

[jiangyiwen]

? 2014/12/23 14:06, Xue jiufei ??:
> Hi jiangyiwen,
> On 2014/12/20 17:39, jiangyiwen wrote:
>> ? 2014/12/20 4:25, Mark Fasheh ??:
>>> 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()
>>>
>> But at this time, it has already called dlm_purge_lockres(). The reasons are as follows:
>> 1) lockres is created in dlm_init_lockres(), it call kref_init(), count is 1;
>> 2) Only when lockres is unused, it will call dlm_lockres_put() twice by dlm_run_purge_list().
>> So dlm_purge_lockres() has been called if the count goes to zero.
>>
>>> 3) dlm_lockres_release() will free the lockres without removing it from the
>>> tracking list. Thus we will have a corrupted list.
>>>
>> Without this scene. dlm_purge_lockres() is called before dlm_lockres_release().
> Once lock resource is inserted into hash list, it should call
> dlm_purge_lockres()->__dlm_unhash_lockres() to put the last ref.
> However, if lock resource is initialized and inserted into tracking
> list but not inserted into hash list, it can happen that
> dlm_lockres_release() will free the lockres without removing it from
> the tracking list.
> So we should remove lockres from tracking list if we call
> dlm_lockres_put() after lockres is created but not inserted into hash
> list yet.
> 
> Thanks,
> Xuejiufei
Thanks, you are right! I will send new version later.
	--Yiwen Jiang

>>> Does that make sense? Am I wrong here?
>>> 	--Mark
>>>
>>> --
>>> Mark Fasheh
>>>
>>> .
>>>
>>
>>
>>
>> _______________________________________________
>> Ocfs2-devel mailing list
>> Ocfs2-devel at oss.oracle.com
>> https://oss.oracle.com/mailman/listinfo/ocfs2-devel
>>
> 
> 
> 
> .
>