[Gluster-devel] Regarding doing away with refkeeper in locks xlator
Pranith Kumar Karampuri
pkarampu at redhat.com
Fri Jun 6 05:17:17 UTC 2014
On 06/06/2014 10:43 AM, Anand Avati wrote:
>
>
>
> On Thu, Jun 5, 2014 at 9:54 PM, Pranith Kumar Karampuri
> <pkarampu at redhat.com <mailto:pkarampu at redhat.com>> wrote:
>
>
> On 06/06/2014 10:02 AM, Anand Avati wrote:
>> On Thu, Jun 5, 2014 at 7:52 PM, Pranith Kumar Karampuri
>> <pkarampu at redhat.com <mailto:pkarampu at redhat.com>> wrote:
>>
>>>
>>> This sounds a bit complicated. I think there is a much
>>> simpler solution:
>>>
>>> - First, make update_refkeeper() check for blocked locks
>>> (which I mentioned as "optional" previously)
>>>
>>> - Make grant_blocked_locks() double up and do the job of
>>> update_refkeeper() internally.
>>>
>>> Something which looks like this:
>>>
>>> diff --git a/xlators/features/locks/src/common.c
>>> b/xlators/features/locks/src/common.c
>>> index f6c71c1..38df385 100644
>>> --- a/xlators/features/locks/src/common.c
>>> +++ b/xlators/features/locks/src/common.c
>>> @@ -126,8 +126,14 @@ __pl_inode_is_empty (pl_inode_t *pl_inode)
>>> if (!list_empty (&dom->entrylk_list))
>>> is_empty = 0;
>>> + if (!list_empty (&dom->blocked_entrylks))
>>> + is_empty = 0;
>>> +
>>> if (!list_empty (&dom->inodelk_list))
>>> is_empty = 0;
>>> +
>>> + if (!list_empty (&dom->blocked_inodelks))
>>> + is_empty = 0;
>>> }
>>> return is_empty;
>>> @@ -944,12 +950,18 @@ grant_blocked_locks (xlator_t *this,
>>> pl_inode_t *pl_inode)
>>> struct list_head granted_list;
>>> posix_lock_t *tmp = NULL;
>>> posix_lock_t *lock = NULL;
>>> + inode_t *unref = NULL;
>>> INIT_LIST_HEAD (&granted_list);
>>> pthread_mutex_lock (&pl_inode->mutex);
>>> {
>>> __grant_blocked_locks (this, pl_inode, &granted_list);
>>> +
>>> + if (__pl_inode_is_empty (pl_inode) &&
>>> pl_inode->refkeeper) {
>>> + unref = pl_inode->refkeeper;
>>> + pl_inode->refkeeper = NULL;
>>> + }
>>> }
>>> pthread_mutex_unlock (&pl_inode->mutex);
>>> @@ -965,6 +977,9 @@ grant_blocked_locks (xlator_t *this,
>>> pl_inode_t *pl_inode)
>>> GF_FREE (lock);
>>> }
>>> + if (unref)
>>> + inode_unref (unref);
>>> +
>>> return;
>>> }
>>>
>>>
>>> This should make pl_disconnect_cbk() pretty much race free
>>> w.r.t refkpeer. Thoughts?
>> Lets say C1 is doing pl_inodelk_client_cleanup. After the
>> second for-loop(All granted and blocked locks are out of the
>> domain) if an unlock on the final granted lock on that inode
>> from client C2 completes, refkeeper would be set to NULL and
>> unrefed leading to zero refs on that inode i.e. pl_forget
>> will also happen. In 3rd for-loop pl_inode is already freed
>> and leads to free'd memory access and will crash.
>>
>>
>>
>> We also need:
>>
>> diff --git a/xlators/features/locks/src/inodelk.c b/xlators/features/locks/src/inodelk.c
>> index c76cb7f..2aceb8a 100644
>> --- a/xlators/features/locks/src/inodelk.c
>> +++ b/xlators/features/locks/src/inodelk.c
>> @@ -494,13 +494,13 @@ pl_inodelk_client_cleanup (xlator_t *this, pl_ctx_t *ctx)
>>
>> dom = get_domain (pl_inode, l->volume);
>>
>> - grant_blocked_inode_locks (this, pl_inode, dom);
>> -
>> pthread_mutex_lock (&pl_inode->mutex);
>> {
>> __pl_inodelk_unref (l);
>> }
>> pthread_mutex_unlock (&pl_inode->mutex);
>> +
>> + grant_blocked_inode_locks (this, pl_inode, dom);
>> }
>>
>> return 0;
>>
>> Missed this in the last patch.
> It still doesn't solve the problem I described earlier. By the
> time it executes this third loop refkeeper is already unreffed
> when C2 unlocks.
>
>
>
> Right, we will need to introduce an "in_cleanup" counter, if set
> pl_update_refkeeper() should not unref. Increment the in_cleanup() in
> the first lookup, and decrement it in the last loop, just before
> calling grant_blocked_locks() (along with the patches in my last 2 mails)
s/first lookup/first loop/ ?
Pranith
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