Re: [Intel-gfx] [PATCH] drm/i915/gt: Fix -EDEADLK handling regression

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 30-06-2021 om 18:44 schreef Ville Syrjala:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> The conversion to ww mutexes failed to address the fence code which
> already returns -EDEADLK when we run out of fences. Ww mutexes on
> the other hand treat -EDEADLK as an internal errno value indicating
> a need to restart the operation due to a deadlock. So now when the
> fence code returns -EDEADLK the higher level code erroneously
> restarts everything instead of returning the error to userspace
> as is expected.
>
> To remedy this let's switch the fence code to use a different errno
> value for this. -ENOBUFS seems like a semi-reasonable unique choice.
> Apart from igt the only user of this I could find is sna, and even
> there all we do is dump the current fence registers from debugfs
> into the X server log. So no user visible functionality is affected.
> If we really cared about preserving this we could of course convert
> back to -EDEADLK higher up, but doesn't seem like that's worth
> the hassle here.
>
> Not quite sure which commit specifically broke this, but I'll
> just attribute it to the general gem ww mutex work.
>
> Cc: stable@vger.kernel.org
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@intel.com>
> Testcase: igt/gem_pread/exhaustion
> Testcase: igt/gem_pwrite/basic-exhaustion
> Testcase: igt/gem_fenced_exec_thrash/too-many-fences
> Fixes: 80f0b679d6f0 ("drm/i915: Add an implementation for i915_gem_ww_ctx locking, v2.")
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
> index cac7f3f44642..f8948de72036 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
> @@ -348,7 +348,7 @@ static struct i915_fence_reg *fence_find(struct i915_ggtt *ggtt)
>  	if (intel_has_pending_fb_unpin(ggtt->vm.i915))
>  		return ERR_PTR(-EAGAIN);
>  
> -	return ERR_PTR(-EDEADLK);
> +	return ERR_PTR(-ENOBUFS);
>  }
>  
>  int __i915_vma_pin_fence(struct i915_vma *vma)

Makes sense..

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

Is it a slightly more reent commit? Might probably be the part that converts execbuffer to use ww locks.

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