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Date:   Thu, 14 Jul 2022 20:49:48 -0700
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To:     Kees Cook <keescook@chromium.org>,
        WeiXiong Liao <gmpy.liaowx@gmail.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>
From:   Florian Fainelli <f.fainelli@gmail.com>
Subject: Invalid pstore_blk use?
Cc:     Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Kamal Dasu <kdasu.kdev@gmail.com>
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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?

Thanks!
-- 
Florian