[Bug 87094] [all]igt/drm_read subcases short-buffer-block and short-buffer-nonblock fail

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87094

Chris Wilson <chris at chris-wilson.co.uk> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Chris Wilson <chris at chris-wilson.co.uk> ---
Should be fixed now:

commit b710d754bd4f80be922c40d8c1231d20f8e55e09
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Thu Dec 4 21:03:25 2014 +0000

    drm: Make drm_read() more robust against multithreaded races

    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>
    Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
    Reviewed-by: Takashi Iwai <tiwai at suse.de>
    Testcase: igt/drm_read
    Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

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