linux-kernel - Re: [REGRESSION][PATCH] Revert "pstore: migrate to crypto acomp interface"

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Date:   Fri, 30 Sep 2022 09:39:10 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Kees Cook <keescook@...omium.org>, Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-kernel@...r.kernel.org, regressions@...ts.linux.dev,
        linux-fsdevel@...r.kernel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Thorsten Leemhuis <linux@...mhuis.info>
Subject: Re: [REGRESSION][PATCH] Revert "pstore: migrate to crypto acomp
 interface"

On 30/09/2022 00:29, Kees Cook wrote:
> [...]
> 
> Hi!
> 
> Thanks for looking at this. I wasn't able to reproduce the problem,
> initially. Booting with pstore.backend=ramoops pstore.compress=zstd and
> writing to /dev/pmsg0, after a reboot I'm able to read it back.
> 

Hi Kees, thanks a lot for your attention!
IIUC, compression applies to dmesg only, correct?

> [...] 
> What's your setup for this? I'm using emulated NVDIMM through qemu for
> a ramoops backend. But trying this with the EFI backend (booting
> undef EFI with pstore.backend=efi), I _do_ see the problem. That's
> weird... I suspect there's some back interaction with buffer size
> differences between ramoops and EFI & deflate and zstd.
> 
> And I can confirm EFI+zstd with the acomp change reverted fixes it.
> 

I'm using qemu but was able to use real HW (Steam Deck). In both cases,
kernel is not using the entire RAM ("mem=" parameter, for example) so we
can use a bit for ramoops. Also, both setups are UEFI, hence I can also
use efi_pstore.

> [...] 
> Hm, it's possible this was just sent directly to me? If that's true, I
> apologize for not re-posting it to lkml. I suspect I didn't notice at
> the time that it wasn't CCed to a list.

No need for apologies, thanks for the clarification! How about if we add
a mailing list in the pstore entry on MAINTAINERS file, since it's just
composed for you and 3 other people now? I mean, "officially" speaking,
it should be enough to send a patch for the 4 maintainers with no list
in CC, and that's bad for achieving purposes. What list should be the
best, fsdevel? Lkml?

> 
> No worries! Whatever the case, there's always -stable updates. :)

Heheh you're right! But for something like this (pstore/dmesg
compression broke for the most backends), I'd be glad if we could fix it
before the release.
Cheers,

Guilherme