Re: [PATCH 5/6] lightnvm: pblk: free up mempool allocation for erases correctly

From: Javier GonzÃlez
Date: Tue Oct 03 2017 - 02:42:44 EST

> On 2 Oct 2017, at 19.18, Rakesh Pandit <rakesh@xxxxxxxxxx> wrote:
> On Mon, Oct 02, 2017 at 03:25:10PM +0300, Rakesh Pandit wrote:
>> On Mon, Oct 02, 2017 at 02:09:35PM +0200, Javier GonzÃlez wrote:
>>>> On 1 Oct 2017, at 15.25, Rakesh Pandit <rakesh@xxxxxxxxxx> wrote:
>>>> While separating read and erase mempools in 22da65a1b pblk_g_rq_cache
>>>> was used two times to set aside memory both for erase and read
>>>> requests. Because same kmem cache is used repeatedly a single call to
>>>> kmem_cache_destroy wouldn't deallocate everything. Repeatedly doing
>>>> loading and unloading of pblk modules would eventually result in some
>>>> leak.
>>>> The fix is to really use separate kmem cache and track it
>>>> appropriately.
>>>> Fixes: 22da65a1b ("lightnvm: pblk: decouple read/erase mempools")
>>>> Signed-off-by: Rakesh Pandit <rakesh@xxxxxxxxxx>
>>> I'm not sure I follow this logic. I assume that you're thinking of the
>>> refcount on kmem_cache. During cache creation, all is good; if a
>>> different cache creation fails, destruction is guaranteed, since the
>>> refcount is 0. On tear down (pblk_core_free), we destroy the mempools
>>> associated to the caches. In this case, the refcount goes to 0 too, as
>>> we destroy the 2 mempools. So I don't see where the leak can happen. Am
>>> I missing something?
>>> In any case, Jens reported some bugs on the mempools, where we did not
>>> guarantee forward progress. Here you can find the original discussion
>>> and the mempool audit [1]. Would be good if you reviewed these.
>>> [1]
>> Thanks, yes makes sense to follow up in patch thread. I will respond
>> to above questions there later today.
> I wasn't thinking it right in addition to looking at test results from
> a incorrectly instrumented debugged version.
> I went through the series you pointed and all seem okay to me now.
> Please drop this patch.



Attachment: signature.asc
Description: Message signed with OpenPGP