linux-kernel - Re: [PATCH RFC] lightnvm: pblk: fix crash in pblk_end_partial

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Message-Id: <FE25456B-A63E-4601-960D-96F519250B8C@javigon.com>
Date:   Thu, 14 Mar 2019 07:16:12 -0700
From:   Javier González <javier@...igon.com>
To:     "Konopko, Igor J" <igor.j.konopko@...el.com>
Cc:     Hans Holmberg <hans@...tronix.com>,
        Matias Bjørling <mb@...htnvm.io>,
        Klaus Birkelund Jensen <klaus.jensen@...xlabs.com>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hans Holmberg <hans.holmberg@...xlabs.com>
Subject: Re: [PATCH RFC] lightnvm: pblk: fix crash in pblk_end_partial_read
 due to multipage bvecs

> On 14 Mar 2019, at 06.49, Igor Konopko <igor.j.konopko@...el.com> wrote:
> 
> While reading this patch, idea came to my mind - maybe it would be simply better to get rid of partial read handling from pblk in current form at all and use bio_split() & bio_chain() combination instead?
> 
> This would definitely reduce a number of this 'kind of complicated' code inside pblk and let block layer help us with that. Even that the performance of such a requests could be a little worse (few smaller IOs instead of single vector IO), I believe that partial read is more a corner case, then a typical use case, so maybe this would be a path to go.
> 
> Let me know what you think about such an approach - I can make a patch with that if you want.

I agree with Igor.

As I mentioned offline, we should fix this in a way that survives
further changes in struct bio; either making pblk handling visible to
the outside or rethinking the whole thing.

Igor: If you can send a patch you mention, it would be great. I have
been trying the helper approach for some time, but it is too specific,
as fixing holes in the bvec breaks the bio advance-only semantics. Your
approach seems much better.

Thanks,
Javier

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