On Thu, Jul 09, 2015 at 03:30:57PM +0100, Tomas Elf wrote:
> The hang checker needs to inspect whether or not the ring request list is empty
> as well as if the given engine has reached or passed the most recently
> submitted request. The problem with this is that the hang checker cannot grab
> the struct_mutex, which is required in order to safely inspect requests since
> requests might be deallocated during inspection. In the past we've had kernel
> panics due to this very unsynchronized access in the hang checker.
>
> One solution to this problem is to not inspect the requests directly since
> we're only interested in the seqno of the most recently submitted request - not
> the request itself. Instead the seqno of the most recently submitted request is
> stored separately, which the hang checker then inspects, circumventing the
> issue of synchronization from the hang checker entirely.
>
> v2 (Chris Wilson):
> - Pass current engine seqno to ring_idle() from i915_hangcheck_elapsed() rather
> than compute it over again.
> - Remove extra whitespace.
>
> Issue: VIZ-5998
> Signed-off-by: Tomas Elf <tomas.elf@xxxxxxxxx>
Yup, that is a nice simple fix by partially reverting the
s/seqno/requests/ change (and improving upon it in the process).
We should mention
Fixes commit 44cdd6d219bc64f6810b8ed0023a4d4db9e0fe68
Author: John Harrison <John.C.Harrison@xxxxxxxxx>
Date: Mon Nov 24 18:49:40 2014 +0000
drm/i915: Convert 'ring_idle()' to use requests not seqnos
and
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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