| Message ID | 20221028194649.1130223-3-John.C.Harrison@Intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fix for two GuC issues | expand |
On 28/10/2022 20:46, John.C.Harrison@Intel.com wrote: > From: John Harrison <John.C.Harrison@Intel.com> > > The engine busyness stats has a worker function to do things like > 64bit extend the 32bit hardware counters. The GuC's reset prepare > function flushes out this worker function to ensure no corruption > happens during the reset. Unforunately, the worker function has an > infinite wait for active resets to finish before doing its work. Thus > a deadlock would occur if the worker function had actually started > just as the reset starts. > > Update the worker to abort if a reset is in progress rather than > waiting for it to complete. It will still acquire the reset lock in > the case where a reset was not already in progress. So the processing > is still safe from corruption, but the deadlock can no longer occur. > > Signed-off-by: John Harrison <John.C.Harrison@Intel.com> > --- > drivers/gpu/drm/i915/gt/intel_reset.c | 15 ++++++++++++++- > drivers/gpu/drm/i915/gt/intel_reset.h | 1 + > drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 6 ++++-- > 3 files changed, 19 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c > index 3159df6cdd492..2f48c6e4420ea 100644 > --- a/drivers/gpu/drm/i915/gt/intel_reset.c > +++ b/drivers/gpu/drm/i915/gt/intel_reset.c > @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, > intel_runtime_pm_put(gt->uncore->rpm, wakeref); > } > > -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) > +static int _intel_gt_reset_trylock(struct intel_gt *gt, int *srcu, bool retry) > { > might_lock(>->reset.backoff_srcu); > might_sleep(); > @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) > while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { > rcu_read_unlock(); > > + if (!retry) > + return -EBUSY; > + > if (wait_event_interruptible(gt->reset.queue, > !test_bit(I915_RESET_BACKOFF, > >->reset.flags))) Would it be more obvious to rename the existing semantics to intel_gt_reset_interruptible(), while the flavour you add in this patch truly is trylock? I am not sure, since it's all a bit special, but trylock sure feels confusing if it can sleep forever... Regards, Tvrtko > @@ -1429,6 +1432,16 @@ int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) > return 0; > } > > +int intel_gt_reset_trylock_noretry(struct intel_gt *gt, int *srcu) > +{ > + return _intel_gt_reset_trylock(gt, srcu, false); > +} > + > +int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) > +{ > + return _intel_gt_reset_trylock(gt, srcu, true); > +} > + > void intel_gt_reset_unlock(struct intel_gt *gt, int tag) > __releases(>->reset.backoff_srcu) > { > diff --git a/drivers/gpu/drm/i915/gt/intel_reset.h b/drivers/gpu/drm/i915/gt/intel_reset.h > index adc734e673870..7f863726eb6a2 100644 > --- a/drivers/gpu/drm/i915/gt/intel_reset.h > +++ b/drivers/gpu/drm/i915/gt/intel_reset.h > @@ -38,6 +38,7 @@ int __intel_engine_reset_bh(struct intel_engine_cs *engine, > > void __i915_request_reset(struct i915_request *rq, bool guilty); > > +int __must_check intel_gt_reset_trylock_noretry(struct intel_gt *gt, int *srcu); > int __must_check intel_gt_reset_trylock(struct intel_gt *gt, int *srcu); > void intel_gt_reset_unlock(struct intel_gt *gt, int tag); > > 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 941613be3b9dd..1fa1bc7dde3df 100644 > --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c > +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c > @@ -1401,9 +1401,11 @@ static void guc_timestamp_ping(struct work_struct *wrk) > > /* > * Synchronize with gt reset to make sure the worker does not > - * corrupt the engine/guc stats. > + * corrupt the engine/guc stats. NB: can't actually block waiting > + * for a reset to complete as the reset requires flushing out > + * any running worker thread. So waiting would deadlock. > */ > - ret = intel_gt_reset_trylock(gt, &srcu); > + ret = intel_gt_reset_trylock_noretry(gt, &srcu); > if (ret) > return; >
On 31/10/2022 10:09, Tvrtko Ursulin wrote: > > On 28/10/2022 20:46, John.C.Harrison@Intel.com wrote: >> From: John Harrison <John.C.Harrison@Intel.com> >> >> The engine busyness stats has a worker function to do things like >> 64bit extend the 32bit hardware counters. The GuC's reset prepare >> function flushes out this worker function to ensure no corruption >> happens during the reset. Unforunately, the worker function has an >> infinite wait for active resets to finish before doing its work. Thus >> a deadlock would occur if the worker function had actually started >> just as the reset starts. >> >> Update the worker to abort if a reset is in progress rather than >> waiting for it to complete. It will still acquire the reset lock in >> the case where a reset was not already in progress. So the processing >> is still safe from corruption, but the deadlock can no longer occur. >> >> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> >> --- >> drivers/gpu/drm/i915/gt/intel_reset.c | 15 ++++++++++++++- >> drivers/gpu/drm/i915/gt/intel_reset.h | 1 + >> drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 6 ++++-- >> 3 files changed, 19 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c >> b/drivers/gpu/drm/i915/gt/intel_reset.c >> index 3159df6cdd492..2f48c6e4420ea 100644 >> --- a/drivers/gpu/drm/i915/gt/intel_reset.c >> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c >> @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, >> intel_runtime_pm_put(gt->uncore->rpm, wakeref); >> } >> -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) >> +static int _intel_gt_reset_trylock(struct intel_gt *gt, int *srcu, >> bool retry) >> { >> might_lock(>->reset.backoff_srcu); >> might_sleep(); >> @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt *gt, >> int *srcu) >> while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { >> rcu_read_unlock(); >> + if (!retry) >> + return -EBUSY; >> + >> if (wait_event_interruptible(gt->reset.queue, >> !test_bit(I915_RESET_BACKOFF, >> >->reset.flags))) > > Would it be more obvious to rename the existing semantics to > intel_gt_reset_interruptible(), while the flavour you add in this patch > truly is trylock? I am not sure, since it's all a bit special, but > trylock sure feels confusing if it can sleep forever... Oh and might_sleep() shouldn't be there with the trylock version - I mean any flavour of the real trylock. Regards, Tvrtko
On 10/31/2022 05:51, Tvrtko Ursulin wrote: > On 31/10/2022 10:09, Tvrtko Ursulin wrote: >> On 28/10/2022 20:46, John.C.Harrison@Intel.com wrote: >>> From: John Harrison <John.C.Harrison@Intel.com> >>> >>> The engine busyness stats has a worker function to do things like >>> 64bit extend the 32bit hardware counters. The GuC's reset prepare >>> function flushes out this worker function to ensure no corruption >>> happens during the reset. Unforunately, the worker function has an >>> infinite wait for active resets to finish before doing its work. Thus >>> a deadlock would occur if the worker function had actually started >>> just as the reset starts. >>> >>> Update the worker to abort if a reset is in progress rather than >>> waiting for it to complete. It will still acquire the reset lock in >>> the case where a reset was not already in progress. So the processing >>> is still safe from corruption, but the deadlock can no longer occur. >>> >>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> >>> --- >>> drivers/gpu/drm/i915/gt/intel_reset.c | 15 >>> ++++++++++++++- >>> drivers/gpu/drm/i915/gt/intel_reset.h | 1 + >>> drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 6 ++++-- >>> 3 files changed, 19 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c >>> b/drivers/gpu/drm/i915/gt/intel_reset.c >>> index 3159df6cdd492..2f48c6e4420ea 100644 >>> --- a/drivers/gpu/drm/i915/gt/intel_reset.c >>> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c >>> @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, >>> intel_runtime_pm_put(gt->uncore->rpm, wakeref); >>> } >>> -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) >>> +static int _intel_gt_reset_trylock(struct intel_gt *gt, int *srcu, >>> bool retry) >>> { >>> might_lock(>->reset.backoff_srcu); >>> might_sleep(); >>> @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt >>> *gt, int *srcu) >>> while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { >>> rcu_read_unlock(); >>> + if (!retry) >>> + return -EBUSY; >>> + >>> if (wait_event_interruptible(gt->reset.queue, >>> !test_bit(I915_RESET_BACKOFF, >>> >->reset.flags))) >> >> Would it be more obvious to rename the existing semantics to >> intel_gt_reset_interruptible(), while the flavour you add in this >> patch truly is trylock? I am not sure, since it's all a bit special, >> but trylock sure feels confusing if it can sleep forever... To me, it would seem totally more obvious to have a function called 'trylock' not wait forever until it can manage to acquire the lock. However, according to '2caffbf1176256 drm/i915: Revoke mmaps and prevent access to fence registers across reset', the current behaviour is exactly how the code was originally written and intended. It hasn't just mutated into some confused evolution a thousand patches later. So I figure there is some subtle but important reason why it was named how it is named and yet does what it does. Therefore it seemed safest to not change it unnecessarily. > > Oh and might_sleep() shouldn't be there with the trylock version - I > mean any flavour of the real trylock. You mean if the code is split into two completely separate functions? Or do you just mean to wrap the might_sleep() call with 'if(!retry)'? And just to be totally clear, the unconditional call to rcu_read_lock() is not something that can sleep? One doesn't need a might_sleep() before doing that lock? John. > > Regards, > > Tvrtko
On 31/10/2022 18:30, John Harrison wrote: > On 10/31/2022 05:51, Tvrtko Ursulin wrote: >> On 31/10/2022 10:09, Tvrtko Ursulin wrote: >>> On 28/10/2022 20:46, John.C.Harrison@Intel.com wrote: >>>> From: John Harrison <John.C.Harrison@Intel.com> >>>> >>>> The engine busyness stats has a worker function to do things like >>>> 64bit extend the 32bit hardware counters. The GuC's reset prepare >>>> function flushes out this worker function to ensure no corruption >>>> happens during the reset. Unforunately, the worker function has an >>>> infinite wait for active resets to finish before doing its work. Thus >>>> a deadlock would occur if the worker function had actually started >>>> just as the reset starts. >>>> >>>> Update the worker to abort if a reset is in progress rather than >>>> waiting for it to complete. It will still acquire the reset lock in >>>> the case where a reset was not already in progress. So the processing >>>> is still safe from corruption, but the deadlock can no longer occur. >>>> >>>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> >>>> --- >>>> drivers/gpu/drm/i915/gt/intel_reset.c | 15 >>>> ++++++++++++++- >>>> drivers/gpu/drm/i915/gt/intel_reset.h | 1 + >>>> drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 6 ++++-- >>>> 3 files changed, 19 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c >>>> b/drivers/gpu/drm/i915/gt/intel_reset.c >>>> index 3159df6cdd492..2f48c6e4420ea 100644 >>>> --- a/drivers/gpu/drm/i915/gt/intel_reset.c >>>> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c >>>> @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, >>>> intel_runtime_pm_put(gt->uncore->rpm, wakeref); >>>> } >>>> -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) >>>> +static int _intel_gt_reset_trylock(struct intel_gt *gt, int *srcu, >>>> bool retry) >>>> { >>>> might_lock(>->reset.backoff_srcu); >>>> might_sleep(); >>>> @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt >>>> *gt, int *srcu) >>>> while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { >>>> rcu_read_unlock(); >>>> + if (!retry) >>>> + return -EBUSY; >>>> + >>>> if (wait_event_interruptible(gt->reset.queue, >>>> !test_bit(I915_RESET_BACKOFF, >>>> >->reset.flags))) >>> >>> Would it be more obvious to rename the existing semantics to >>> intel_gt_reset_interruptible(), while the flavour you add in this >>> patch truly is trylock? I am not sure, since it's all a bit special, >>> but trylock sure feels confusing if it can sleep forever... > To me, it would seem totally more obvious to have a function called > 'trylock' not wait forever until it can manage to acquire the lock. > However, according to '2caffbf1176256 drm/i915: Revoke mmaps and prevent > access to fence registers across reset', the current behaviour is > exactly how the code was originally written and intended. It hasn't just > mutated into some confused evolution a thousand patches later. So I > figure there is some subtle but important reason why it was named how it > is named and yet does what it does. Therefore it seemed safest to not > change it unnecessarily. Yeah I looked at that but honestly I don't see the trylock semantics anywhere. The only failure to lock path comes from wait_event_interruptible. It could have easily been just a naming mishap. And I find adding a retry parameter to something called trylock makes this even more non-intuitive and would personally rather rename it all. Proof in the pudding is that the trylock naming did bite during development and review of the code this patch is now fixing. I do however understand your point about a degree of uncertainty but my feeling is to rather err on the side of obvious naming. Shall we ask for a third opinion? >> Oh and might_sleep() shouldn't be there with the trylock version - I >> mean any flavour of the real trylock. > You mean if the code is split into two completely separate functions? Or > do you just mean to wrap the might_sleep() call with 'if(!retry)'? > > And just to be totally clear, the unconditional call to rcu_read_lock() > is not something that can sleep? One doesn't need a might_sleep() before > doing that lock? Corrrect, rcu_read_lock() can not sleep - it just disables preemption. So leaving the unconditional might_sleep() would have opportunity for false positives. Regards, Tvrtko
On 11/1/2022 02:58, Tvrtko Ursulin wrote: > On 31/10/2022 18:30, John Harrison wrote: >> On 10/31/2022 05:51, Tvrtko Ursulin wrote: >>> On 31/10/2022 10:09, Tvrtko Ursulin wrote: >>>> On 28/10/2022 20:46, John.C.Harrison@Intel.com wrote: >>>>> From: John Harrison <John.C.Harrison@Intel.com> >>>>> >>>>> The engine busyness stats has a worker function to do things like >>>>> 64bit extend the 32bit hardware counters. The GuC's reset prepare >>>>> function flushes out this worker function to ensure no corruption >>>>> happens during the reset. Unforunately, the worker function has an >>>>> infinite wait for active resets to finish before doing its work. Thus >>>>> a deadlock would occur if the worker function had actually started >>>>> just as the reset starts. >>>>> >>>>> Update the worker to abort if a reset is in progress rather than >>>>> waiting for it to complete. It will still acquire the reset lock in >>>>> the case where a reset was not already in progress. So the processing >>>>> is still safe from corruption, but the deadlock can no longer occur. >>>>> >>>>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> >>>>> --- >>>>> drivers/gpu/drm/i915/gt/intel_reset.c | 15 >>>>> ++++++++++++++- >>>>> drivers/gpu/drm/i915/gt/intel_reset.h | 1 + >>>>> drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 6 ++++-- >>>>> 3 files changed, 19 insertions(+), 3 deletions(-) >>>>> >>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c >>>>> b/drivers/gpu/drm/i915/gt/intel_reset.c >>>>> index 3159df6cdd492..2f48c6e4420ea 100644 >>>>> --- a/drivers/gpu/drm/i915/gt/intel_reset.c >>>>> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c >>>>> @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, >>>>> intel_runtime_pm_put(gt->uncore->rpm, wakeref); >>>>> } >>>>> -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) >>>>> +static int _intel_gt_reset_trylock(struct intel_gt *gt, int >>>>> *srcu, bool retry) >>>>> { >>>>> might_lock(>->reset.backoff_srcu); >>>>> might_sleep(); >>>>> @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt >>>>> *gt, int *srcu) >>>>> while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { >>>>> rcu_read_unlock(); >>>>> + if (!retry) >>>>> + return -EBUSY; >>>>> + >>>>> if (wait_event_interruptible(gt->reset.queue, >>>>> !test_bit(I915_RESET_BACKOFF, >>>>> >->reset.flags))) >>>> >>>> Would it be more obvious to rename the existing semantics to >>>> intel_gt_reset_interruptible(), while the flavour you add in this >>>> patch truly is trylock? I am not sure, since it's all a bit >>>> special, but trylock sure feels confusing if it can sleep forever... >> To me, it would seem totally more obvious to have a function called >> 'trylock' not wait forever until it can manage to acquire the lock. >> However, according to '2caffbf1176256 drm/i915: Revoke mmaps and >> prevent access to fence registers across reset', the current >> behaviour is exactly how the code was originally written and >> intended. It hasn't just mutated into some confused evolution a >> thousand patches later. So I figure there is some subtle but >> important reason why it was named how it is named and yet does what >> it does. Therefore it seemed safest to not change it unnecessarily. > > Yeah I looked at that but honestly I don't see the trylock semantics > anywhere. The only failure to lock path comes from > wait_event_interruptible. It could have easily been just a naming mishap. > > And I find adding a retry parameter to something called trylock makes > this even more non-intuitive and would personally rather rename it > all. Proof in the pudding is that the trylock naming did bite during > development and review of the code this patch is now fixing. > > I do however understand your point about a degree of uncertainty but > my feeling is to rather err on the side of obvious naming. Shall we > ask for a third opinion? Umesh had commented (internally) that the naming seems wrong and would be good to change it. So we already have a third :). To be clear, you are thinking to keep the wrappers but rename to intel_gt_reset_trylock() [retry = false] and intel_gt_reset_interruptible() [retry = true]? Which will obviously involve updating all but one existing user to use the interruptible name as the existing name will change behaviour in a backwards breaking manner. John. > >>> Oh and might_sleep() shouldn't be there with the trylock version - I >>> mean any flavour of the real trylock. >> You mean if the code is split into two completely separate functions? >> Or do you just mean to wrap the might_sleep() call with 'if(!retry)'? >> >> And just to be totally clear, the unconditional call to >> rcu_read_lock() is not something that can sleep? One doesn't need a >> might_sleep() before doing that lock? > > Corrrect, rcu_read_lock() can not sleep - it just disables preemption. > So leaving the unconditional might_sleep() would have opportunity for > false positives. > > Regards, > > Tvrtko
On 01/11/2022 16:56, John Harrison wrote: > On 11/1/2022 02:58, Tvrtko Ursulin wrote: >> On 31/10/2022 18:30, John Harrison wrote: >>> On 10/31/2022 05:51, Tvrtko Ursulin wrote: >>>> On 31/10/2022 10:09, Tvrtko Ursulin wrote: >>>>> On 28/10/2022 20:46, John.C.Harrison@Intel.com wrote: >>>>>> From: John Harrison <John.C.Harrison@Intel.com> >>>>>> >>>>>> The engine busyness stats has a worker function to do things like >>>>>> 64bit extend the 32bit hardware counters. The GuC's reset prepare >>>>>> function flushes out this worker function to ensure no corruption >>>>>> happens during the reset. Unforunately, the worker function has an >>>>>> infinite wait for active resets to finish before doing its work. Thus >>>>>> a deadlock would occur if the worker function had actually started >>>>>> just as the reset starts. >>>>>> >>>>>> Update the worker to abort if a reset is in progress rather than >>>>>> waiting for it to complete. It will still acquire the reset lock in >>>>>> the case where a reset was not already in progress. So the processing >>>>>> is still safe from corruption, but the deadlock can no longer occur. >>>>>> >>>>>> Signed-off-by: John Harrison <John.C.Harrison@Intel.com> >>>>>> --- >>>>>> drivers/gpu/drm/i915/gt/intel_reset.c | 15 >>>>>> ++++++++++++++- >>>>>> drivers/gpu/drm/i915/gt/intel_reset.h | 1 + >>>>>> drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 6 ++++-- >>>>>> 3 files changed, 19 insertions(+), 3 deletions(-) >>>>>> >>>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c >>>>>> b/drivers/gpu/drm/i915/gt/intel_reset.c >>>>>> index 3159df6cdd492..2f48c6e4420ea 100644 >>>>>> --- a/drivers/gpu/drm/i915/gt/intel_reset.c >>>>>> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c >>>>>> @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, >>>>>> intel_runtime_pm_put(gt->uncore->rpm, wakeref); >>>>>> } >>>>>> -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) >>>>>> +static int _intel_gt_reset_trylock(struct intel_gt *gt, int >>>>>> *srcu, bool retry) >>>>>> { >>>>>> might_lock(>->reset.backoff_srcu); >>>>>> might_sleep(); >>>>>> @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt >>>>>> *gt, int *srcu) >>>>>> while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { >>>>>> rcu_read_unlock(); >>>>>> + if (!retry) >>>>>> + return -EBUSY; >>>>>> + >>>>>> if (wait_event_interruptible(gt->reset.queue, >>>>>> !test_bit(I915_RESET_BACKOFF, >>>>>> >->reset.flags))) >>>>> >>>>> Would it be more obvious to rename the existing semantics to >>>>> intel_gt_reset_interruptible(), while the flavour you add in this >>>>> patch truly is trylock? I am not sure, since it's all a bit >>>>> special, but trylock sure feels confusing if it can sleep forever... >>> To me, it would seem totally more obvious to have a function called >>> 'trylock' not wait forever until it can manage to acquire the lock. >>> However, according to '2caffbf1176256 drm/i915: Revoke mmaps and >>> prevent access to fence registers across reset', the current >>> behaviour is exactly how the code was originally written and >>> intended. It hasn't just mutated into some confused evolution a >>> thousand patches later. So I figure there is some subtle but >>> important reason why it was named how it is named and yet does what >>> it does. Therefore it seemed safest to not change it unnecessarily. >> >> Yeah I looked at that but honestly I don't see the trylock semantics >> anywhere. The only failure to lock path comes from >> wait_event_interruptible. It could have easily been just a naming mishap. >> >> And I find adding a retry parameter to something called trylock makes >> this even more non-intuitive and would personally rather rename it >> all. Proof in the pudding is that the trylock naming did bite during >> development and review of the code this patch is now fixing. >> >> I do however understand your point about a degree of uncertainty but >> my feeling is to rather err on the side of obvious naming. Shall we >> ask for a third opinion? > Umesh had commented (internally) that the naming seems wrong and would > be good to change it. So we already have a third :). > > To be clear, you are thinking to keep the wrappers but rename to > intel_gt_reset_trylock() [retry = false] and > intel_gt_reset_interruptible() [retry = true]? Which will obviously > involve updating all but one existing user to use the interruptible name > as the existing name will change behaviour in a backwards breaking manner. Yes, intel_gt_reset_lock_interruptible and intel_gt_reset_trylock. I don't get the behaviour breaking part? Only the name will change. And amount of churn does not seem a problem: $ grep intel_gt_reset_trylock -r . ./gem/i915_gem_mman.c: ret = intel_gt_reset_trylock(ggtt->vm.gt, &srcu); ./gt/uc/intel_guc_submission.c: ret = intel_gt_reset_trylock(gt, &srcu); ./gt/intel_reset.c:int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) ./gt/intel_reset.h:int __must_check intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) Regards, Tvrtko > > John. > >> >>>> Oh and might_sleep() shouldn't be there with the trylock version - I >>>> mean any flavour of the real trylock. >>> You mean if the code is split into two completely separate functions? >>> Or do you just mean to wrap the might_sleep() call with 'if(!retry)'? >>> >>> And just to be totally clear, the unconditional call to >>> rcu_read_lock() is not something that can sleep? One doesn't need a >>> might_sleep() before doing that lock? >> >> Corrrect, rcu_read_lock() can not sleep - it just disables preemption. >> So leaving the unconditional might_sleep() would have opportunity for >> false positives. >> >> Regards, >> >> Tvrtko >
diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c index 3159df6cdd492..2f48c6e4420ea 100644 --- a/drivers/gpu/drm/i915/gt/intel_reset.c +++ b/drivers/gpu/drm/i915/gt/intel_reset.c @@ -1407,7 +1407,7 @@ void intel_gt_handle_error(struct intel_gt *gt, intel_runtime_pm_put(gt->uncore->rpm, wakeref); } -int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) +static int _intel_gt_reset_trylock(struct intel_gt *gt, int *srcu, bool retry) { might_lock(>->reset.backoff_srcu); might_sleep(); @@ -1416,6 +1416,9 @@ int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) while (test_bit(I915_RESET_BACKOFF, >->reset.flags)) { rcu_read_unlock(); + if (!retry) + return -EBUSY; + if (wait_event_interruptible(gt->reset.queue, !test_bit(I915_RESET_BACKOFF, >->reset.flags))) @@ -1429,6 +1432,16 @@ int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) return 0; } +int intel_gt_reset_trylock_noretry(struct intel_gt *gt, int *srcu) +{ + return _intel_gt_reset_trylock(gt, srcu, false); +} + +int intel_gt_reset_trylock(struct intel_gt *gt, int *srcu) +{ + return _intel_gt_reset_trylock(gt, srcu, true); +} + void intel_gt_reset_unlock(struct intel_gt *gt, int tag) __releases(>->reset.backoff_srcu) { diff --git a/drivers/gpu/drm/i915/gt/intel_reset.h b/drivers/gpu/drm/i915/gt/intel_reset.h index adc734e673870..7f863726eb6a2 100644 --- a/drivers/gpu/drm/i915/gt/intel_reset.h +++ b/drivers/gpu/drm/i915/gt/intel_reset.h @@ -38,6 +38,7 @@ int __intel_engine_reset_bh(struct intel_engine_cs *engine, void __i915_request_reset(struct i915_request *rq, bool guilty); +int __must_check intel_gt_reset_trylock_noretry(struct intel_gt *gt, int *srcu); int __must_check intel_gt_reset_trylock(struct intel_gt *gt, int *srcu); void intel_gt_reset_unlock(struct intel_gt *gt, int tag); 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 941613be3b9dd..1fa1bc7dde3df 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -1401,9 +1401,11 @@ static void guc_timestamp_ping(struct work_struct *wrk) /* * Synchronize with gt reset to make sure the worker does not - * corrupt the engine/guc stats. + * corrupt the engine/guc stats. NB: can't actually block waiting + * for a reset to complete as the reset requires flushing out + * any running worker thread. So waiting would deadlock. */ - ret = intel_gt_reset_trylock(gt, &srcu); + ret = intel_gt_reset_trylock_noretry(gt, &srcu); if (ret) return;