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

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Date:   Wed, 5 Apr 2023 19:11:24 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Luis Chamberlain <mcgrof@...nel.org>, 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
Cc:     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 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 :)


> +		/* 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 ...

> +
> +		/* 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.

> +}
> +
>   /*
>    * We try to place it in the list now to make sure it's unique before

Besides, LGTM.

-- 
Thanks,

David / dhildenb