linux-kernel - Re: Invalid pstore

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Date:   Tue, 9 Aug 2022 11:35:08 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Kees Cook <keescook@...omium.org>,
        WeiXiong Liao <gmpy.liaowx@...il.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Kamal Dasu <kdasu.kdev@...il.com>
Subject: Re: Invalid pstore_blk use?

Hi Kees, WeiXiong,

On 7/14/22 20:49, Florian Fainelli wrote:
> Hi Kees, WeiXiong,
> 
> I am trying to make use of pstore_blk which is BTW exactly what I had 
> been looking for to store panic/console logs onto an eMMC partition.
> 
> Using the 5.10 kernel plus:
> 
> 7e2e92e9861b Revert "mark pstore-blk as broken"
> 01c28bc8f389 pstore/blk: Use the normal block device I/O path
> 2a7507999638 pstore/blk: remove {un,}register_pstore_blk
> fef0b337cd25 pstore/zone: cap the maximum device size
> 
> or the android13-5.15 (at Merge 5.15.40 into android13-5.15) kernel with 
> no changes and using:
> 
> mount -t pstore pstore /sys/fs/pstore
> modprobe pstore_blk blkdev=/dev/mmcblk1p9 best_effort=yes
> 
> upon triggering a crash with:
> 
> echo c > /proc/sysrq-trigger
> 
> and rebooting and remounting the pstore filesystem and loading 
> pstore_blk, I only have:
> 
> # ls /sys/fs/pstore/
> console-pstore_blk-0
> 
> which contains the entire console log up to, but excluding the crash. 
> The kernel does show that pstore_blk was used for all 3 types of kmsg, 
> pmsg and console:
> 
> [   28.649514] pstore_zone: capping size to 128MiB
> [   28.712894] pstore_zone: registered pstore_blk as backend for 
> kmsg(Oops) pmsg console
> [   28.721145] pstore: Using crash dump compression: deflate
> [   28.906253] printk: console [pstore_blk-1] enabled
> [   28.911229] pstore: Registered pstore_blk as persistent store backend
> [   28.917735] pstore_blk: attached pstore_blk:/dev/mmcblk1p9 
> (134217728) (no dedicated panic_write!)
> 
> there is no automatic reboot upon panic, so I just tend to reboot after 
> 2-3 seconds manually. The kernel is configured with the default 
> CONFIG_PSTORE_* options.
> 
> Is the observed behavior a limitation of the best_effort mode? If so, do 
> we have any plans to implementing a non-best effort mode for eMMC devices?

Any feedback on my email? I did try to get kernel panics to be dumped 
out to a dedicated /dev/mtdblock* partition for which there ought to be 
support for mtd->panic_write, but it still did not work any better. Is 
there something obvious that I am missing which prevents kernel panics 
from being logged?

Thank you!
-- 
Florian