linux-kernel - Re: [PATCH v3] kernel/module: Reschedule while waiting for modules to finish loading

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Message-ID: <90e18809-2b70-52d8-00b3-9c16768db9ad@redhat.com>
Date:   Wed, 1 May 2019 17:26:50 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...nel.org>
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        David Arcari <darcari@...hat.com>
Subject: Re: [PATCH v3] kernel/module: Reschedule while waiting for modules to
 finish loading



On 4/30/19 6:22 PM, Prarit Bhargava wrote:
> On a s390 z14 LAR with 2 cpus about stalls about 3% of the time while
> loading the s390_trng.ko module.
> 
> Add a reschedule point to the loop that waits for modules to complete
> loading.
> 
> v3: cleanup Fixes line.

Jessica, even with this additional patch there appears to be some other issues
in the module code that are causing significant delays in boot up on large
systems.

Please revert these fixes from linux-next & modules-next.  I apologize for the
extra work but I think it is for the best until I come up with a more complete &
better tested patch.

FWIW, the logic in the original patch is correct.  It's just that there's, as
Heiko discovered, some poor scheduling, etc., that is impacting the module
loading code after these changes.

Again, my apologies,

P.

> 
> Reported-by: Heiko Carstens <heiko.carstens@...ibm.com>
> Fixes: f9a75c1d717f ("modules: Only return -EEXIST for modules that have finished loading")
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> ---
>  kernel/module.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/module.c b/kernel/module.c
> index 410eeb7e4f1d..48748cfec991 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3585,6 +3585,7 @@ static int add_unformed_module(struct module *mod)
>  					       finished_loading(mod->name));
>  			if (err)
>  				goto out_unlocked;
> +			cond_resched();
>  			goto again;
>  		}
>  		err = -EEXIST;
>