linux-kernel - Re: [PATCH] staging: bcm2835-camera: Avoid apotential sleep while holding a spin

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Date:   Mon, 24 Jun 2019 08:37:18 +0200
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     eric@...olt.net, stefan.wahren@...e.com,
        gregkh@...uxfoundation.org, f.fainelli@...il.com,
        rjui@...adcom.com, sbranden@...adcom.com,
        bcm-kernel-feedback-list@...adcom.com, tuomas.tynkkynen@....fi,
        inf.braun@....de, tobias.buettner@....de, hofrat@...dl.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] staging: bcm2835-camera: Avoid apotential sleep while
 holding a spin_lock

On Mon, Jun 24, 2019 at 07:33:51AM +0200, Christophe JAILLET wrote:
> Do not allocate memory with GFP_KERNEL when holding a spin_lock, it may
> sleep. Use GFP_NOWAIT instead.
>

checking for this in the rest of the kernel with a cocci spatch
<snip>
virtual report

@nonatomic@
position p;
identifier var;
@@

  spin_lock(...)
  ... when != spin_unlock(...)
* var = idr_alloc@p(...,GFP_KERNEL);
  ... when != spin_unlock(...)
  spin_unlock(...);
<snip>
this seems to be the only instance of this specific problem.

> Fixes: 950fd867c635 ("staging: bcm2835-camera: Replace open-coded idr with a struct idr.")

The GFP_KERNEL actually was there befor this patch so not sure if this Fixes
ref is correct - I think the GFP_KERNEL was introduced in:
4e6bafdfb9f3 ("staging: bcm2835_camera: Use a mapping table for context field of mmal_msg_header")

> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Reviewed-by: Nicholas Mc Guire <hofrat@...dl.org>

> ---
>  drivers/staging/vc04_services/bcm2835-camera/mmal-vchiq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/vc04_services/bcm2835-camera/mmal-vchiq.c b/drivers/staging/vc04_services/bcm2835-camera/mmal-vchiq.c
> index 16af735af5c3..438d548c6e24 100644
> --- a/drivers/staging/vc04_services/bcm2835-camera/mmal-vchiq.c
> +++ b/drivers/staging/vc04_services/bcm2835-camera/mmal-vchiq.c
> @@ -186,7 +186,7 @@ get_msg_context(struct vchiq_mmal_instance *instance)
>  	 */
>  	spin_lock(&instance->context_map_lock);
>  	handle = idr_alloc(&instance->context_map, msg_context,
> -			   0, 0, GFP_KERNEL);
> +			   0, 0, GFP_NOWAIT);
>  	spin_unlock(&instance->context_map_lock);
>  
>  	if (handle < 0) {
> -- 
> 2.20.1
>