[Intel-gfx] [PATCH] drm: Make drm_read() more robust against multithreaded races

[Daniel Vetter]

On Fri, Dec 05, 2014 at 09:42:35AM +0100, Takashi Iwai wrote:
> At Thu,  4 Dec 2014 21:03:25 +0000,
> Chris Wilson wrote:
> > 
> > The current implementation of drm_read() faces a number of issues:
> > 
> > 1. Upon an error, it consumes the event which may lead to the client
> > blocking.
> > 2. Upon an error, it forgets about events already copied
> > 3. If it fails to copy a single event with O_NONBLOCK it falls into a
> > infinite loop of reporting EAGAIN.
> > 3. There is a race between multiple waiters and blocking reads of the
> > events list.
> > 
> > Here, we inline drm_dequeue_event() into drm_read() so that we can take
> > the spinlock around the list walking and event copying, and importantly
> > reorder the error handling to avoid the issues above.
> > 
> > Cc: Takashi Iwai <tiwai at suse.de>
> 
> Reviewed-by: Takashi Iwai <tiwai at suse.de>

Merged to drm-misc with the tag for the drm_read testcase added. Thanks
for the patch&reivew.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch