Re: Deadlock in intel_user_framebuffer_destroy()

Jani Nikula
2015-06-15T06:46:05Z

On Wed, 03 Jun 2015, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> On Wed, Jun 03, 2015 at 03:43:32PM +0200, Lukas Wunner wrote:
>> Hi,
>>
>> a deadlock was introduced by commit 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
>>
>> Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Date: Fri Jun 13 11:10:53 2014 +0300
>>
>> drm/i915: Add locking around framebuffer_references--
>>
>>
>> The commit amended intel_display.c:intel_user_framebuffer_destroy() with
>> mutex_lock(&dev->struct_mutex).
>>
>> A few weeks prior Chris Wilson had amended intel_fbdev.c:intelfb_create()
>> with a call to drm_framebuffer_unreference() while &dev->struct_mutex is
>> locked (commit edd586fe705e819bc711b5ed7194a0b6f9f1a7e1, "drm/i915: Discard
>> BIOS framebuffers too small to accommodate chosen mode").
>>
>
> Just move the mutex_lock down a step.

Lucas, did you try this?

BR,
Jani.

>
> t a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 6372cfc..a9b8c43 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -209,8 +209,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
> int size, ret;
> bool prealloc = false;
>
> - mutex_lock(&dev->struct_mutex);
> -
> if (intel_fb &&
> (sizes->fb_width > intel_fb->base.width ||
> sizes->fb_height > intel_fb->base.height)) {
> @@ -221,6 +219,9 @@ static int intelfb_create(struct drm_fb_helper *helper,
> drm_framebuffer_unreference(&intel_fb->base);
> intel_fb = ifbdev->fb = NULL;
> }
> +
> + mutex_lock(&dev->struct_mutex);
> +
> if (!intel_fb || WARN_ON(!intel_fb->obj)) {
> DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
> ret = intelfb_alloc(helper, sizes);
>
> --
> Chris Wilson, Intel Open Source Technology Centre
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--
Jani Nikula, Intel Open Source Technology Center