[Ocfs2-devel] [PATCH 1/1] Ocfs2: Handle invalid lock_res in lockres_seq_start() for dlmdebug.c

[tristan <tristan.ye@oracle.com>]

Sunil Mushran wrote:
> On 09/09/2010 02:16 AM, Tristan Ye wrote:
>> In lockres_seq_start() of dlmdebug.c, when you looking at following
>> piece of codes:
>>
>> list_for_each_entry(res, track_list, tracking) {
>>     if (&res->tracking ==&dlm->tracking_list)
>>         res = NULL;
>>     else
>>         dlm_lockres_get(res);
>>     break;
>> }
>>
>> ...
>>
>> if (res) {
>>     spin_lock(&res->spinlock);
>>     dump_lockres(res, dl->dl_buf, dl->dl_len - 1);
>>     spin_unlock(&res->spinlock);
>> } else
>>     dl = NULL;
>>
>> One thought can come to you that, in the case of 'an-empty-list', 
>> cursor 'res'
>> here is not an INVALID pointer for real dlm_lock_resource object, it 
>> is nothing
>> than a fake address figured out by arbitary 'container_of()' way, the 
>> patch tries
>> to check track_list, and avoid accessing an invalid pointer if the 
>> list is empty,
>> it fixes following oops:
>>
>> http://oss.oracle.com/bugzilla/show_bug.cgi?id=1287
>>
>> Signed-off-by: Tristan Ye<tristan.ye@oracle.com>
>> ---
>>    
>
> Such a detailed description is only required if the bug fix
> is complicated. This is a simple fix. Just say that this handles
> the case in which the dlm->tracking_list is empty and mention
> the bz.
>

Yeah, kind of...

>>   fs/ocfs2/dlm/dlmdebug.c |    7 +++++++
>>   1 files changed, 7 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/ocfs2/dlm/dlmdebug.c b/fs/ocfs2/dlm/dlmdebug.c
>> index 5efdd37..06d668a 100644
>> --- a/fs/ocfs2/dlm/dlmdebug.c
>> +++ b/fs/ocfs2/dlm/dlmdebug.c
>> @@ -639,6 +639,12 @@ static void *lockres_seq_start(struct seq_file 
>> *m, loff_t *pos)
>>       else
>>           track_list =&dlm->tracking_list;
>>
>> +    if (list_empty(track_list)) {
>> +        dl = NULL;
>> +        spin_unlock(&dlm->track_lock);
>> +        goto bail;
>> +    }
>> +
>>    
>
> You should add this check as part of the else block above so
> that we check for empty list only at the start.

So we just don't need to check list 'oldres->tracking'?

>
>>       list_for_each_entry(res, track_list, tracking) {
>>           if (&res->tracking ==&dlm->tracking_list)
>>               res = NULL;
>> @@ -660,6 +666,7 @@ static void *lockres_seq_start(struct seq_file 
>> *m, loff_t *pos)
>>       } else
>>           dl = NULL;
>>
>> +bail:
>>       /* passed to seq_show */
>>       return dl;
>>   }
>>    
>