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SubjectRe: [PATCH 1/2] fs/ocfs2/dlm: Eliminate update of list_for_each_entry loop cursor
I think it got lost in the shuffle. We had decided to use the list_for_each().
The code is simpler to understand than the other proposed fix.

Joel, do you want me to send a patch?

On 11/02/2011 12:39 AM, Dan Carpenter wrote:
> What ever happened with this? The bug is still there in the latest
> kernel.
>
> I think from previous discussion about this that we only ever have
> one lock so lock->ml.cookie is always equal to ml->cookie and we
> never set lock to NULL. So we never actually hit the NULL deref.
> But it should probably still be cleaned up.
>
> regards,
> dan carpenter
>
> On Wed, Aug 11, 2010 at 05:03:56PM -0700, Joel Becker wrote:
>> On Sat, Aug 07, 2010 at 11:09:13AM +0200, Julia Lawall wrote:
>>> From: Julia Lawall<julia@diku.dk>
>>>
>>> list_for_each_entry uses its first argument to move from one element to the
>>> next, so modifying it can break the iteration.
>> Thanks for catching the bug. It was introduced by 800deef3
>> [ocfs2: use list_for_each_entry where benefical]. I blame Christoph.
>>
>>> diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
>>> index 9dfaac7..7084a11 100644
>>> --- a/fs/ocfs2/dlm/dlmrecovery.c
>>> +++ b/fs/ocfs2/dlm/dlmrecovery.c
>>> @@ -1792,10 +1792,10 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
>>> for (j = DLM_GRANTED_LIST; j<= DLM_BLOCKED_LIST; j++) {
>>> tmpq = dlm_list_idx_to_ptr(res, j);
>>> list_for_each_entry(lock, tmpq, list) {
>>> - if (lock->ml.cookie != ml->cookie)
>>> + if (lock->ml.cookie != ml->cookie) {
>>> lock = NULL;
>>> - else
>>> break;
>>> + }
>>> }
>>> if (lock)
>>> break;
>> However, this is not the correct solution. The goal of the
>> original code, which used to use list_for_each(), was to leave lock
>> non-NULL if the cookie was found. Your version merely exits the loop on
>> the first non-matching entry, always leaving lock==NULL if there is a
>> non-matching entry.
>> One possible solution is to return the original code:
>>
>> --8<-----------------------------------------------------------------
>> @@ -1747,7 +1747,7 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
>> struct dlm_migratable_lockres *mres)
>> {
>> struct dlm_migratable_lock *ml;
>> - struct list_head *queue;
>> + struct list_head *queue, *iter;
>> struct list_head *tmpq = NULL;
>> struct dlm_lock *newlock = NULL;
>> struct dlm_lockstatus *lksb = NULL;
>> @@ -1791,11 +1791,12 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
>> spin_lock(&res->spinlock);
>> for (j = DLM_GRANTED_LIST; j<= DLM_BLOCKED_LIST; j++) {
>> tmpq = dlm_list_idx_to_ptr(res, j);
>> - list_for_each_entry(lock, tmpq, list) {
>> - if (lock->ml.cookie != ml->cookie)
>> - lock = NULL;
>> - else
>> + list_for_each(iter, tmpq) {
>> + lock = list_entry(iter, struct dlm_lock, list);
>> +
>> + if (lock->ml.cookie == ml->cookie)
>> break;
>> + lock = NULL;
>> }
>> if (lock)
>> break;
>> -->8-----------------------------------------------------------------
>>
>> Another approach would be to keep list_for_each_entry() around,
>> but use a better check for entry existence:
>>
>> --8<-----------------------------------------------------------------
>> @@ -1792,13 +1792,12 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
>> for (j = DLM_GRANTED_LIST; j<= DLM_BLOCKED_LIST; j++) {
>> tmpq = dlm_list_idx_to_ptr(res, j);
>> list_for_each_entry(lock, tmpq, list) {
>> - if (lock->ml.cookie != ml->cookie)
>> - lock = NULL;
>> - else
>> + if (lock->ml.cookie == ml->cookie)
>> break;
>> }
>> - if (lock)
>> + if (&lock->list != tmpq)
>> break;
>> + lock = NULL;
>> }
>>
>> /* lock is always created locally first, and
>> -->8-----------------------------------------------------------------
>>
>> I think I like the second one better. Sunil, what do you think?
>>
>> Joel
>>
>> --
>>
>> Life's Little Instruction Book #335
>>
>> "Every so often, push your luck."
>>
>> Joel Becker
>> Consulting Software Developer
>> Oracle
>> E-mail: joel.becker@oracle.com
>> Phone: (650) 506-8127
>> --
>> To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at http://vger.kernel.org/majordomo-info.html



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