Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Message-ID: <fbbd0a8d-2ef4-4a39-4b75-354918e85778@igalia.com>
Date:   Wed, 18 May 2022 10:16:20 -0300
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.0
Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list
Content-Language: en-US
To:     Petr Mladek <pmladek@suse.com>
Cc:     David Gow <davidgow@google.com>, Evan Green <evgreen@chromium.org>,
        Julius Werner <jwerner@chromium.org>,
        Scott Branden <scott.branden@broadcom.com>,
        bcm-kernel-feedback-list@broadcom.com,
        Sebastian Reichel <sre@kernel.org>, linux-pm@vger.kernel.org,
        Florian Fainelli <f.fainelli@gmail.com>,
        akpm@linux-foundation.org, bhe@redhat.com,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-edac@vger.kernel.org,
        linux-hyperv@vger.kernel.org, linux-leds@vger.kernel.org,
        linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org,
        linux-remoteproc@vger.kernel.org, linux-s390@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-um@lists.infradead.org,
        linux-xtensa@linux-xtensa.org, netdev@vger.kernel.org,
        openipmi-developer@lists.sourceforge.net, rcu@vger.kernel.org,
        sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org,
        x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net,
        halves@canonical.com, fabiomirmar@gmail.com,
        alejandro.j.jimenez@oracle.com, andriy.shevchenko@linux.intel.com,
        arnd@arndb.de, bp@alien8.de, corbet@lwn.net,
        d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com,
        dyoung@redhat.com, feng.tang@intel.com, gregkh@linuxfoundation.org,
        mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com,
        jgross@suse.com, john.ogness@linutronix.de, keescook@chromium.org,
        luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com,
        paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org,
        senozhatsky@chromium.org, stern@rowland.harvard.edu,
        tglx@linutronix.de, vgoyal@redhat.com, vkuznets@redhat.com,
        will@kernel.org, Alexander Gordeev <agordeev@linux.ibm.com>,
        Andrea Parri <parri.andrea@gmail.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        "David S. Miller" <davem@davemloft.net>,
        Dexuan Cui <decui@microsoft.com>,
        Doug Berger <opendmb@gmail.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Hari Bathini <hbathini@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Justin Chen <justinpopo6@gmail.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Lee Jones <lee.jones@linaro.org>,
        Markus Mayer <mmayer@broadcom.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Mihai Carabas <mihai.carabas@oracle.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Paul Mackerras <paulus@samba.org>, Pavel Machek <pavel@ucw.cz>,
        Shile Zhang <shile.zhang@linux.alibaba.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Wang ShaoBo <bobo.shaobowang@huawei.com>,
        Wei Liu <wei.liu@kernel.org>,
        zhenwei pi <pizhenwei@bytedance.com>
References: <20220427224924.592546-1-gpiccoli@igalia.com>
 <20220427224924.592546-20-gpiccoli@igalia.com> <YoJZVZl/MH0KiE/J@alley>
 <ad082ce7-db50-13bb-3dbb-9b595dfa78be@igalia.com> <YoOpyW1+q+Z5as78@alley>
 <YoSnGmBJ3kYs5WMf@alley>
From:   "Guilherme G. Piccoli" <gpiccoli@igalia.com>
In-Reply-To: <YoSnGmBJ3kYs5WMf@alley>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 18/05/2022 04:58, Petr Mladek wrote:
> [...]
>> I does similar things like kmsg_dump() so it should be called in
>> the same location (after info notifier list and before kdump).
>>
>> A solution might be to put it at these notifiers at the very
>> end of the "info" list or make extra "dump" notifier list.
> 
> I just want to point out that the above idea has problems.
> Notifiers storing kernel log need to be treated as kmsg_dump().
> In particular, we would  need to know if there are any.
> We do not need to call "info" notifier list before kdump
> when there is no kernel log dumper registered.
> 

Notifiers respect the priority concept, which is just a number that
orders the list addition (and the list is called in order).

I've used the last position to panic_print() [in patch 25] - one idea
here is to "reserve" the last position (represented by INT_MIN) for
notifiers that act like kmsg_dump(). I couldn't find any IIRC, but that
doesn't prevent us to save this position and comment about that.

Makes sense to you ?
Cheers!