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

13 Jul 2021

On Thu, Jul 1, 2021 at 9:07 AM Maarten Lankhorst
maarten.lankhorst@linux.intel.com wrote:
...
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.
- please cc: dri-devel on anything gem/gt related.
- this should probably be ENOSPC or something like that for at least a
seeming retention of errno consistentcy:
https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#recommended-ioctl-ret...
Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

    

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

-Daniel