On Thu, Aug 19, 2021 at 02:31:51PM -0700, Daniele Ceraolo Spurio wrote:
>
>
> On 8/18/2021 11:16 PM, Matthew Brost wrote:
> > A small race that could result in incorrect accounting of the number
> > of outstanding G2H. Basically prior to this patch we did not increment
> > the number of outstanding G2H if we encoutered a GT reset while sending
> > a H2G. This was incorrect as the context state had already been updated
> > to anticipate a G2H response thus the counter should be incremented.
> >
> > Also always use helper when decrementing this value.
> >
> > Fixes: f4eb1f3fe946 ("drm/i915/guc: Ensure G2H response has space in buffer")
> > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > ---
> > .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 24 ++++++++++---------
> > 1 file changed, 13 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > index 69faa39da178..32c414aa9009 100644
> > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> > @@ -352,6 +352,12 @@ static inline void set_lrc_desc_registered(struct intel_guc *guc, u32 id,
> > xa_unlock_irqrestore(&guc->context_lookup, flags);
> > }
> > +static void decr_outstanding_submission_g2h(struct intel_guc *guc)
> > +{
> > + if (atomic_dec_and_test(&guc->outstanding_submission_g2h))
> > + wake_up_all(&guc->ct.wq);
> > +}
> > +
> > static int guc_submission_send_busy_loop(struct intel_guc *guc,
> > const u32 *action,
> > u32 len,
> > @@ -360,11 +366,13 @@ static int guc_submission_send_busy_loop(struct intel_guc *guc,
> > {
> > int err;
> > - err = intel_guc_send_busy_loop(guc, action, len, g2h_len_dw, loop);
> > -
> > - if (!err && g2h_len_dw)
> > + if (g2h_len_dw)
> > atomic_inc(&guc->outstanding_submission_g2h);
> > + err = intel_guc_send_busy_loop(guc, action, len, g2h_len_dw, loop);
> > + if (err == -EBUSY && g2h_len_dw)
> > + decr_outstanding_submission_g2h(guc);
> > +
>
> here you're special casing -EBUSY, which kind of implies that the caller
> needs to handle this differently, but most callers seem to ignore the return
> code. Is the counter handled somewhere else in case of EBUSY? if so, please
> add a comment about it.
>
Good catch, this is a dead code path. Will delete.
Matt
> Daniele
>
> > return err;
> > }
> > @@ -616,7 +624,7 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
> > init_sched_state(ce);
> > if (pending_enable || destroyed || deregister) {
> > - atomic_dec(&guc->outstanding_submission_g2h);
> > + decr_outstanding_submission_g2h(guc);
> > if (deregister)
> > guc_signal_context_fence(ce);
> > if (destroyed) {
> > @@ -635,7 +643,7 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
> > intel_engine_signal_breadcrumbs(ce->engine);
> > }
> > intel_context_sched_disable_unpin(ce);
> > - atomic_dec(&guc->outstanding_submission_g2h);
> > + decr_outstanding_submission_g2h(guc);
> > spin_lock_irqsave(&ce->guc_state.lock, flags);
> > guc_blocked_fence_complete(ce);
> > spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> > @@ -2583,12 +2591,6 @@ g2h_context_lookup(struct intel_guc *guc, u32 desc_idx)
> > return ce;
> > }
> > -static void decr_outstanding_submission_g2h(struct intel_guc *guc)
> > -{
> > - if (atomic_dec_and_test(&guc->outstanding_submission_g2h))
> > - wake_up_all(&guc->ct.wq);
> > -}
> > -
> > int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
> > const u32 *msg,
> > u32 len)
>
