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

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Message-ID: <ZH3UTOaBD7f5KH6Q@hovoldconsulting.com>
Date:   Mon, 5 Jun 2023 14:25:48 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Petr Pavlu <petr.pavlu@...e.com>, gregkh@...uxfoundation.org,
        rafael@...nel.org, song@...nel.org, lucas.de.marchi@...il.com,
        christophe.leroy@...roup.eu, peterz@...radead.org, rppt@...nel.org,
        dave@...olabs.net, willy@...radead.org, vbabka@...e.cz,
        mhocko@...e.com, dave.hansen@...ux.intel.com,
        colin.i.king@...il.com, jim.cromie@...il.com,
        catalin.marinas@....com, jbaron@...mai.com,
        rick.p.edgecombe@...el.com, yujie.liu@...el.com, david@...hat.com,
        tglx@...utronix.de, hch@....de, patches@...ts.linux.dev,
        linux-modules@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, pmladek@...e.com, prarit@...hat.com,
        lennart@...ttering.net
Subject: Re: [PATCH 2/2] module: add support to avoid duplicates early on load

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

Johan