linux-kernel - Re: [PATCH v2 3/6] module: extract patient module check into helper

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Message-ID: <ZC3P8m1AN5XZNjrP@bombadil.infradead.org>
Date:   Wed, 5 Apr 2023 12:45:54 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     patches@...ts.linux.dev, linux-modules@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, pmladek@...e.com,
        petr.pavlu@...e.com, prarit@...hat.com,
        torvalds@...ux-foundation.org, gregkh@...uxfoundation.org,
        rafael@...nel.org, christophe.leroy@...roup.eu, tglx@...utronix.de,
        peterz@...radead.org, song@...nel.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
Subject: Re: [PATCH v2 3/6] module: extract patient module check into helper

On Wed, Apr 05, 2023 at 07:11:24PM +0200, David Hildenbrand wrote:
> On 05.04.23 04:26, Luis Chamberlain wrote:
> > The patient module check inside add_unformed_module() is large
> > enough as we need it. It is a bit hard to read too, so just
> > move it to a helper and do the inverse checks first to help
> > shift the code and make it easier to read. The new helper then
> > is module_patient_check_exists().
> > 
> > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > ---
> >   kernel/module/main.c | 71 +++++++++++++++++++++++++-------------------
> >   1 file changed, 40 insertions(+), 31 deletions(-)
> > 
> > diff --git a/kernel/module/main.c b/kernel/module/main.c
> > index 98c261928325..8f382580195b 100644
> > --- a/kernel/module/main.c
> > +++ b/kernel/module/main.c
> > @@ -2638,6 +2638,43 @@ static bool finished_loading(const char *name)
> >   	return ret;
> >   }
> > +/* Must be called with module_mutex held */
> > +static int module_patient_check_exists(const char *name)
> > +{
> > +	struct module *old;
> > +	int err = 0;
> > +
> > +	old = find_module_all(name, strlen(name), true);
> > +	if (old == NULL)
> > +		return 0;
> > +
> > +	if (old->state == MODULE_STATE_COMING
> > +	    || old->state == MODULE_STATE_UNFORMED) {
> 
> I never understood why people prefer to prefix the || on a newline. But it
> seems to be a thing in the module/ world :)

Yeah the other way seems better, I'll make it pretty.

> > +		/* Wait in case it fails to load. */
> > +		mutex_unlock(&module_mutex);
> > +		err = wait_event_interruptible(module_wq,
> > +				       finished_loading(name));
> > +		if (err)
> > +			return err;
> 
> You return with the mutex unlocked. The caller will unlock again ...

Fixed now by moving the mutex below up after the wait_event_interruptible(),
thanks.

> > +
> > +		/* The module might have gone in the meantime. */
> > +		mutex_lock(&module_mutex);
> > +		old = find_module_all(name, strlen(name), true);
> > +	}
> > +
> > +	/*
> > +	 * We are here only when the same module was being loaded. Do
> > +	 * not try to load it again right now. It prevents long delays
> > +	 * caused by serialized module load failures. It might happen
> > +	 * when more devices of the same type trigger load of
> > +	 * a particular module.
> > +	 */
> > +	if (old && old->state == MODULE_STATE_LIVE)
> > +		return -EEXIST;
> > +	else
> > +		return -EBUSY;
> 
> You can drop the else and return right away.

Will make it pretty like that, thanks.

  Luis