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

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Message-ID: <20171002122510.GA3946@hercules.tuxera.com>
Date:   Mon, 2 Oct 2017 15:25:11 +0300
From:   Rakesh Pandit <rakesh@...era.com>
To:     Javier González <jg@...htnvm.io>
CC:     Matias Bjørling <mb@...htnvm.io>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] lightnvm: pblk: free up mempool allocation for
 erases correctly

On Mon, Oct 02, 2017 at 02:09:35PM +0200, Javier González wrote:
> > On 1 Oct 2017, at 15.25, Rakesh Pandit <rakesh@...era.com> 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@...era.com>
> > 
> 
> 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] https://www.spinics.net/lists/kernel/msg2602274.html
> 

Thanks, yes makes sense to follow up in patch thread.  I will respond
to above questions there later today.