Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   Valentin Schneider <vschneid@redhat.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        linux-rt-users@vger.kernel.org,
        Eric Biederman <ebiederm@xmission.com>,
        Arnd Bergmann <arnd@arndb.de>, Petr Mladek <pmladek@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Juri Lelli <jlelli@redhat.com>,
        "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>
Subject: Re: [PATCH v2] panic, kexec: Make __crash_kexec() NMI safe
In-Reply-To: <YrUTsJiIQb583fKy@MiWiFi-R3L-srv>
References: <20220620111520.1039685-1-vschneid@redhat.com>
 <YrUTsJiIQb583fKy@MiWiFi-R3L-srv>
Date:   Fri, 24 Jun 2022 14:37:33 +0100
Message-ID: <xhsmhsfnu5giq.mognet@vschneid.remote.csb>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On 24/06/22 09:30, Baoquan He wrote:
> On 06/20/22 at 12:15pm, Valentin Schneider wrote:
>> @@ -94,14 +94,20 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>>  	/*
>>  	 * Because we write directly to the reserved memory region when loading
>>  	 * crash kernels we need a mutex here to prevent multiple crash kernels
>> -	 * from attempting to load simultaneously, and to prevent a crash kernel
>> -	 * from loading over the top of a in use crash kernel.
>> -	 *
>> -	 * KISS: always take the mutex.
>> +	 * from attempting to load simultaneously.
>>  	 */
>>  	if (!mutex_trylock(&kexec_mutex))
>>  		return -EBUSY;
>
> So kexec_mutex is degenerated to only avoid simultaneous loading,
> should we rename to reflect that?, e.g kexec_load_mutex.
>

It's also serializing crash_get_memory_size() and crash_shrink_memory();
more generally it should still be the preferred serialization mechanism as
it's a "proper" lock visible by instrumentation, the atomic variable is a
side character for the NMI case.