Re: [PATCH v2] panic, kexec: Make __crash_kexec() NMI safe

From: Baoquan He <bhe@redhat.com>
To: Valentin Schneider <vschneid@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
Date: Sun, 26 Jun 2022 18:37:24 +0800	[thread overview]
Message-ID: <Yrg25MZNqt+h1FCB@MiWiFi-R3L-srv> (raw)
In-Reply-To: <xhsmhsfnu5giq.mognet@vschneid.remote.csb>

On 06/24/22 at 02:37pm, Valentin Schneider wrote:
> 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.

You are right. I only checked the code comment in this place. Then this
patch looks good to me, thx.

Acked-by: Baoquan He <bhe@redhat.com>