Re: [PATCH 2/2] module: add support to avoid duplicates early on load

From: Johan Hovold <johan@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>,
	Lucas De Marchi <lucas.demarchi@intel.com>,
	Petr Pavlu <petr.pavlu@suse.com>,
	gregkh@linuxfoundation.org, rafael@kernel.org, song@kernel.org,
	lucas.de.marchi@gmail.com, christophe.leroy@csgroup.eu,
	peterz@infradead.org, rppt@kernel.org, dave@stgolabs.net,
	willy@infradead.org, vbabka@suse.cz, mhocko@suse.com,
	dave.hansen@linux.intel.com, colin.i.king@gmail.com,
	jim.cromie@gmail.com, catalin.marinas@arm.com, jbaron@akamai.com,
	rick.p.edgecombe@intel.com, yujie.liu@intel.com,
	david@redhat.com, tglx@linutronix.de, hch@lst.de,
	patches@lists.linux.dev, linux-modules@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	pmladek@suse.com, prarit@redhat.com, lennart@poettering.net
Subject: Re: [PATCH 2/2] module: add support to avoid duplicates early on load
Date: Mon, 5 Jun 2023 14:25:48 +0200	[thread overview]
Message-ID: <ZH3UTOaBD7f5KH6Q@hovoldconsulting.com> (raw)
In-Reply-To: <ZHXEktFq7NPYLtGn@hovoldconsulting.com>

On Tue, May 30, 2023 at 11:40:35AM +0200, Johan Hovold wrote:
> On Mon, May 29, 2023 at 09:55:15PM -0400, Linus Torvalds wrote:
> > On Mon, May 29, 2023 at 11:18 AM Johan Hovold <johan@kernel.org> wrote:
> > >
> > > I took a closer look at some of the modules that failed to load and
> > > noticed a pattern in that they have dependencies that are needed by more
> > > than one device.
> > 
> > Ok, this is a "maybe something like this" RFC series of two patches -
> > one trivial one to re-organize things a bit so that we can then do the
> > real one which uses a filter based on the inode pointer to return an
> > "idempotent return value" for module loads that share the same inode.
> > 
> > It's entirely untested, and since I'm on the road I'm going to not
> > really be able to test it. It compiles for me, and the code looks
> > fairly straightforward, but it's probably buggy.
> > 
> > It's very loosely based on Luis' attempt,  but it
> >  (a) is internal to module loading
> >  (b) uses a reliable cookie
> >  (c) doesn't leave the cookie around randomly for later
> >  (d) has seen absolutely no testing
> > 
> > Put another way: if somebody wants to play with this, please treat it
> > as a starting point, not the final thing. You might need to debug
> > things, and fix silly mistakes.
> 
> With the missing spinlock initialisation fixed:
> 
> -static struct spinlock idem_lock;
> +static DEFINE_SPINLOCK(idem_lock);
> 
> this passes basic smoke testing and allows the X13s to boot.
> 
> It does not seem to have any significant impact on boot time, but it
> avoids some of the unnecessary load attempts as intended:

Took another look at code which modulo some nits like missing spaces
around a + operator and an "ourselfs" typo looks good to me. So with the
spinlock initialisation fixed:

Reviewed-by: Johan Hovold <johan@kernel.org>
Tested-by: Johan Hovold <johan@kernel.org>

Johan