Re: [Intel-gfx] [PATCH 04/27] drm/i915/guc: Take GT PM ref when deregistering context

Tvrtko Ursulin
2021-09-14T08:41:16Z

On 13/09/2021 18:12, Matthew Brost wrote:
> On Mon, Sep 13, 2021 at 10:55:59AM +0100, Tvrtko Ursulin wrote:
>>
>> On 20/08/2021 23:44, Matthew Brost wrote:
>>> Taking a PM reference to prevent intel_gt_wait_for_idle from short
>>> circuiting while a deregister context H2G is in flight.
>>>
>>> FIXME: Move locking / structure changes into different patch
>>>
>>> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
>>> ---
>>> drivers/gpu/drm/i915/gt/intel_context.c | 2 +
>>> drivers/gpu/drm/i915/gt/intel_context_types.h | 13 +-
>>> drivers/gpu/drm/i915/gt/intel_engine_pm.h | 5 +
>>> drivers/gpu/drm/i915/gt/intel_gt_pm.h | 13 ++
>>> .../gpu/drm/i915/gt/uc/abi/guc_actions_abi.h | 1 +
>>> drivers/gpu/drm/i915/gt/uc/intel_guc.h | 46 ++--
>>> .../gpu/drm/i915/gt/uc/intel_guc_debugfs.c | 13 +-
>>> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 212 +++++++++++-------
>>> 8 files changed, 199 insertions(+), 106 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
>>> index adfe49b53b1b..c8595da64ad8 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_context.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
>>> @@ -399,6 +399,8 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
>>> ce->guc_id.id = GUC_INVALID_LRC_ID;
>>> INIT_LIST_HEAD(&ce->guc_id.link);
>>> + INIT_LIST_HEAD(&ce->destroyed_link);
>>> +
>>> /*
>>> * Initialize fence to be complete as this is expected to be complete
>>> * unless there is a pending schedule disable outstanding.
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
>>> index 80bbdc7810f6..fd338a30617e 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
>>> @@ -190,22 +190,29 @@ struct intel_context {
>>> /**
>>> * @id: unique handle which is used to communicate information
>>> * with the GuC about this context, protected by
>>> - * guc->contexts_lock
>>> + * guc->submission_state.lock
>>> */
>>> u16 id;
>>> /**
>>> * @ref: the number of references to the guc_id, when
>>> * transitioning in and out of zero protected by
>>> - * guc->contexts_lock
>>> + * guc->submission_state.lock
>>> */
>>> atomic_t ref;
>>> /**
>>> * @link: in guc->guc_id_list when the guc_id has no refs but is
>>> - * still valid, protected by guc->contexts_lock
>>> + * still valid, protected by guc->submission_state.lock
>>> */
>>> struct list_head link;
>>> } guc_id;
>>> + /**
>>> + * @destroyed_link: link in guc->submission_state.destroyed_contexts, in
>>> + * list when context is pending to be destroyed (deregistered with the
>>> + * GuC), protected by guc->submission_state.lock
>>> + */
>>> + struct list_head destroyed_link;
>>> +
>>> #ifdef CONFIG_DRM_I915_SELFTEST
>>> /**
>>> * @drop_schedule_enable: Force drop of schedule enable G2H for selftest
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.h b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
>>> index 70ea46d6cfb0..17a5028ea177 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.h
>>> @@ -16,6 +16,11 @@ intel_engine_pm_is_awake(const struct intel_engine_cs *engine)
>>> return intel_wakeref_is_active(&engine->wakeref);
>>> }
>>> +static inline void __intel_engine_pm_get(struct intel_engine_cs *engine)
>>> +{
>>> + __intel_wakeref_get(&engine->wakeref);
>>> +}
>>> +
>>> static inline void intel_engine_pm_get(struct intel_engine_cs *engine)
>>> {
>>> intel_wakeref_get(&engine->wakeref);
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.h b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
>>> index d0588d8aaa44..a17bf0d4592b 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.h
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
>>> @@ -41,6 +41,19 @@ static inline void intel_gt_pm_put_async(struct intel_gt *gt)
>>> intel_wakeref_put_async(&gt->wakeref);
>>> }
>>> +#define with_intel_gt_pm(gt, tmp) \
>>> + for (tmp = 1, intel_gt_pm_get(gt); tmp; \
>>> + intel_gt_pm_put(gt), tmp = 0)
>>> +#define with_intel_gt_pm_async(gt, tmp) \
>>> + for (tmp = 1, intel_gt_pm_get(gt); tmp; \
>>> + intel_gt_pm_put_async(gt), tmp = 0)
>>> +#define with_intel_gt_pm_if_awake(gt, tmp) \
>>> + for (tmp = intel_gt_pm_get_if_awake(gt); tmp; \
>>> + intel_gt_pm_put(gt), tmp = 0)
>>> +#define with_intel_gt_pm_if_awake_async(gt, tmp) \
>>> + for (tmp = intel_gt_pm_get_if_awake(gt); tmp; \
>>> + intel_gt_pm_put_async(gt), tmp = 0)
>>> +
>>> static inline int intel_gt_pm_wait_for_idle(struct intel_gt *gt)
>>> {
>>> return intel_wakeref_wait_for_idle(&gt->wakeref);
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h b/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h
>>> index 8ff582222aff..ba10bd374cee 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/abi/guc_actions_abi.h
>>> @@ -142,6 +142,7 @@ enum intel_guc_action {
>>> INTEL_GUC_ACTION_REGISTER_COMMAND_TRANSPORT_BUFFER = 0x4505,
>>> INTEL_GUC_ACTION_DEREGISTER_COMMAND_TRANSPORT_BUFFER = 0x4506,
>>> INTEL_GUC_ACTION_DEREGISTER_CONTEXT_DONE = 0x4600,
>>> + INTEL_GUC_ACTION_REGISTER_CONTEXT_MULTI_LRC = 0x4601,
>>> INTEL_GUC_ACTION_RESET_CLIENT = 0x5507,
>>> INTEL_GUC_ACTION_LIMIT
>>> };
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.h b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> index 6fd2719d1b75..7358883f1540 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.h
>>> @@ -53,21 +53,37 @@ struct intel_guc {
>>> void (*disable)(struct intel_guc *guc);
>>> } interrupts;
>>> - /**
>>> - * @contexts_lock: protects guc_ids, guc_id_list, ce->guc_id.id, and
>>> - * ce->guc_id.ref when transitioning in and out of zero
>>> - */
>>> - spinlock_t contexts_lock;
>>> - /** @guc_ids: used to allocate new guc_ids */
>>> - struct ida guc_ids;
>>> - /** @num_guc_ids: number of guc_ids that can be used */
>>> - u32 num_guc_ids;
>>> - /** @max_guc_ids: max number of guc_ids that can be used */
>>> - u32 max_guc_ids;
>>> - /**
>>> - * @guc_id_list: list of intel_context with valid guc_ids but no refs
>>> - */
>>> - struct list_head guc_id_list;
>>> + struct {
>>> + /**
>>> + * @lock: protects everything in submission_state, ce->guc_id,
>>> + * and ce->destroyed_link
>>> + */
>>> + spinlock_t lock;
>>> + /**
>>> + * @guc_ids: used to allocate new guc_ids
>>> + */
>>> + struct ida guc_ids;
>>> + /** @num_guc_ids: number of guc_ids that can be used */
>>> + u32 num_guc_ids;
>>> + /** @max_guc_ids: max number of guc_ids that can be used */
>>> + u32 max_guc_ids;
>>> + /**
>>> + * @guc_id_list: list of intel_context with valid guc_ids but no
>>> + * refs
>>> + */
>>> + struct list_head guc_id_list;
>>> + /**
>>> + * @destroyed_contexts: list of contexts waiting to be destroyed
>>> + * (deregistered with the GuC)
>>> + */
>>> + struct list_head destroyed_contexts;
>>> + /**
>>> + * @destroyed_worker: worker to deregister contexts, need as we
>>> + * need to take a GT PM reference and can't from destroy
>>> + * function as it might be in an atomic context (no sleeping)
>>> + */
>>> + struct work_struct destroyed_worker;
>>> + } submission_state;
>>> bool submission_supported;
>>> bool submission_selected;
>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_debugfs.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_debugfs.c
>>> index b88d343ee432..27655460ee84 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_debugfs.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_debugfs.c
>>> @@ -78,7 +78,7 @@ static int guc_num_id_get(void *data, u64 *val)
>>> if (!intel_guc_submission_is_used(guc))
>>> return -ENODEV;
>>> - *val = guc->num_guc_ids;
>>> + *val = guc->submission_state.num_guc_ids;
>>> return 0;
>>> }
>>> @@ -86,16 +86,21 @@ static int guc_num_id_get(void *data, u64 *val)
>>> static int guc_num_id_set(void *data, u64 val)
>>> {
>>> struct intel_guc *guc = data;
>>> + unsigned long flags;
>>> if (!intel_guc_submission_is_used(guc))
>>> return -ENODEV;
>>> - if (val > guc->max_guc_ids)
>>> - val = guc->max_guc_ids;
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> +
>>> + if (val > guc->submission_state.max_guc_ids)
>>> + val = guc->submission_state.max_guc_ids;
>>> else if (val < 256)
>>> val = 256;
>>> - guc->num_guc_ids = val;
>>> + guc->submission_state.num_guc_ids = val;
>>> +
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> return 0;
>>> }
>>> 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 68742b612692..f835e06e5f9f 100644
>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
>>> @@ -86,9 +86,9 @@
>>> * submitting at a time. Currently only 1 sched_engine used for all of GuC
>>> * submission but that could change in the future.
>>> *
>>> - * guc->contexts_lock
>>> - * Protects guc_id allocation. Global lock i.e. Only 1 context that uses GuC
>>> - * submission can hold this at a time.
>>> + * guc->submission_state.lock
>>> + * Global lock for GuC submission state. Protects guc_ids and destroyed contexts
>>> + * list.
>>> *
>>> * ce->guc_state.lock
>>> * Protects everything under ce->guc_state. Ensures that a context is in the
>>> @@ -100,7 +100,7 @@
>>> *
>>> * Lock ordering rules:
>>> * sched_engine->lock -> ce->guc_state.lock
>>> - * guc->contexts_lock -> ce->guc_state.lock
>>> + * guc->submission_state.lock -> ce->guc_state.lock
>>> *
>>> * Reset races:
>>> * When a GPU full reset is triggered it is assumed that some G2H responses to
>>> @@ -344,7 +344,7 @@ static struct guc_lrc_desc *__get_lrc_desc(struct intel_guc *guc, u32 index)
>>> {
>>> struct guc_lrc_desc *base = guc->lrc_desc_pool_vaddr;
>>> - GEM_BUG_ON(index >= guc->max_guc_ids);
>>> + GEM_BUG_ON(index >= guc->submission_state.max_guc_ids);
>>> return &base[index];
>>> }
>>> @@ -353,7 +353,7 @@ static struct intel_context *__get_context(struct intel_guc *guc, u32 id)
>>> {
>>> struct intel_context *ce = xa_load(&guc->context_lookup, id);
>>> - GEM_BUG_ON(id >= guc->max_guc_ids);
>>> + GEM_BUG_ON(id >= guc->submission_state.max_guc_ids);
>>> return ce;
>>> }
>>> @@ -363,7 +363,8 @@ static int guc_lrc_desc_pool_create(struct intel_guc *guc)
>>> u32 size;
>>> int ret;
>>> - size = PAGE_ALIGN(sizeof(struct guc_lrc_desc) * guc->max_guc_ids);
>>> + size = PAGE_ALIGN(sizeof(struct guc_lrc_desc) *
>>> + guc->submission_state.max_guc_ids);
>>> ret = intel_guc_allocate_and_map_vma(guc, size, &guc->lrc_desc_pool,
>>> (void **)&guc->lrc_desc_pool_vaddr);
>>> if (ret)
>>> @@ -711,6 +712,7 @@ static void scrub_guc_desc_for_outstanding_g2h(struct intel_guc *guc)
>>> if (deregister)
>>> guc_signal_context_fence(ce);
>>> if (destroyed) {
>>> + intel_gt_pm_put_async(guc_to_gt(guc));
>>> release_guc_id(guc, ce);
>>> __guc_context_destroy(ce);
>>> }
>>> @@ -789,6 +791,8 @@ static void guc_flush_submissions(struct intel_guc *guc)
>>> spin_unlock_irqrestore(&sched_engine->lock, flags);
>>> }
>>> +static void guc_flush_destroyed_contexts(struct intel_guc *guc);
>>> +
>>> void intel_guc_submission_reset_prepare(struct intel_guc *guc)
>>> {
>>> if (unlikely(!guc_submission_initialized(guc))) {
>>> @@ -805,6 +809,7 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
>>> spin_unlock_irq(&guc_to_gt(guc)->irq_lock);
>>> flush_work(&guc->ct.requests.worker);
>>> + guc_flush_destroyed_contexts(guc);
>>> scrub_guc_desc_for_outstanding_g2h(guc);
>>> }
>>> @@ -1102,6 +1107,8 @@ void intel_guc_submission_reset_finish(struct intel_guc *guc)
>>> intel_gt_unpark_heartbeats(guc_to_gt(guc));
>>> }
>>> +static void destroyed_worker_func(struct work_struct *w);
>>> +
>>> /*
>>> * Set up the memory resources to be shared with the GuC (via the GGTT)
>>> * at firmware loading time.
>>> @@ -1124,9 +1131,11 @@ int intel_guc_submission_init(struct intel_guc *guc)
>>> xa_init_flags(&guc->context_lookup, XA_FLAGS_LOCK_IRQ);
>>> - spin_lock_init(&guc->contexts_lock);
>>> - INIT_LIST_HEAD(&guc->guc_id_list);
>>> - ida_init(&guc->guc_ids);
>>> + spin_lock_init(&guc->submission_state.lock);
>>> + INIT_LIST_HEAD(&guc->submission_state.guc_id_list);
>>> + ida_init(&guc->submission_state.guc_ids);
>>> + INIT_LIST_HEAD(&guc->submission_state.destroyed_contexts);
>>> + INIT_WORK(&guc->submission_state.destroyed_worker, destroyed_worker_func);
>>> return 0;
>>> }
>>> @@ -1137,6 +1146,7 @@ void intel_guc_submission_fini(struct intel_guc *guc)
>>> return;
>>> guc_lrc_desc_pool_destroy(guc);
>>> + guc_flush_destroyed_contexts(guc);
>>> i915_sched_engine_put(guc->sched_engine);
>>> }
>>> @@ -1191,15 +1201,16 @@ static void guc_submit_request(struct i915_request *rq)
>>> static int new_guc_id(struct intel_guc *guc)
>>> {
>>> - return ida_simple_get(&guc->guc_ids, 0,
>>> - guc->num_guc_ids, GFP_KERNEL |
>>> + return ida_simple_get(&guc->submission_state.guc_ids, 0,
>>> + guc->submission_state.num_guc_ids, GFP_KERNEL |
>>> __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
>>> }
>>> static void __release_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>> {
>>> if (!context_guc_id_invalid(ce)) {
>>> - ida_simple_remove(&guc->guc_ids, ce->guc_id.id);
>>> + ida_simple_remove(&guc->submission_state.guc_ids,
>>> + ce->guc_id.id);
>>> reset_lrc_desc(guc, ce->guc_id.id);
>>> set_context_guc_id_invalid(ce);
>>> }
>>> @@ -1211,9 +1222,9 @@ static void release_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>> {
>>> unsigned long flags;
>>> - spin_lock_irqsave(&guc->contexts_lock, flags);
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> __release_guc_id(guc, ce);
>>> - spin_unlock_irqrestore(&guc->contexts_lock, flags);
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> }
>>> static int steal_guc_id(struct intel_guc *guc)
>>> @@ -1221,10 +1232,10 @@ static int steal_guc_id(struct intel_guc *guc)
>>> struct intel_context *ce;
>>> int guc_id;
>>> - lockdep_assert_held(&guc->contexts_lock);
>>> + lockdep_assert_held(&guc->submission_state.lock);
>>> - if (!list_empty(&guc->guc_id_list)) {
>>> - ce = list_first_entry(&guc->guc_id_list,
>>> + if (!list_empty(&guc->submission_state.guc_id_list)) {
>>> + ce = list_first_entry(&guc->submission_state.guc_id_list,
>>> struct intel_context,
>>> guc_id.link);
>>> @@ -1249,7 +1260,7 @@ static int assign_guc_id(struct intel_guc *guc, u16 *out)
>>> {
>>> int ret;
>>> - lockdep_assert_held(&guc->contexts_lock);
>>> + lockdep_assert_held(&guc->submission_state.lock);
>>> ret = new_guc_id(guc);
>>> if (unlikely(ret < 0)) {
>>> @@ -1271,7 +1282,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>> GEM_BUG_ON(atomic_read(&ce->guc_id.ref));
>>> try_again:
>>> - spin_lock_irqsave(&guc->contexts_lock, flags);
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> might_lock(&ce->guc_state.lock);
>>> @@ -1286,7 +1297,7 @@ static int pin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>> atomic_inc(&ce->guc_id.ref);
>>> out_unlock:
>>> - spin_unlock_irqrestore(&guc->contexts_lock, flags);
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> /*
>>> * -EAGAIN indicates no guc_id are available, let's retire any
>>> @@ -1322,11 +1333,12 @@ static void unpin_guc_id(struct intel_guc *guc, struct intel_context *ce)
>>> if (unlikely(context_guc_id_invalid(ce)))
>>> return;
>>> - spin_lock_irqsave(&guc->contexts_lock, flags);
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> if (!context_guc_id_invalid(ce) && list_empty(&ce->guc_id.link) &&
>>> !atomic_read(&ce->guc_id.ref))
>>> - list_add_tail(&ce->guc_id.link, &guc->guc_id_list);
>>> - spin_unlock_irqrestore(&guc->contexts_lock, flags);
>>> + list_add_tail(&ce->guc_id.link,
>>> + &guc->submission_state.guc_id_list);
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> }
>>> static int __guc_action_register_context(struct intel_guc *guc,
>>> @@ -1841,11 +1853,30 @@ static void guc_context_sched_disable(struct intel_context *ce)
>>> static void guc_lrc_desc_unpin(struct intel_context *ce)
>>> {
>>> struct intel_guc *guc = ce_to_guc(ce);
>>> + struct intel_gt *gt = guc_to_gt(guc);
>>> + unsigned long flags;
>>> + bool disabled;
>>> + GEM_BUG_ON(!intel_gt_pm_is_awake(gt));
>>> GEM_BUG_ON(!lrc_desc_registered(guc, ce->guc_id.id));
>>> GEM_BUG_ON(ce != __get_context(guc, ce->guc_id.id));
>>> GEM_BUG_ON(context_enabled(ce));
>>> + /* Seal race with Reset */
>>> + spin_lock_irqsave(&ce->guc_state.lock, flags);
>>> + disabled = submission_disabled(guc);
>>> + if (likely(!disabled)) {
>>> + __intel_gt_pm_get(gt);
>>> + set_context_destroyed(ce);
>>> + clr_context_registered(ce);
>>> + }
>>> + spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>>> + if (unlikely(disabled)) {
>>> + release_guc_id(guc, ce);
>>> + __guc_context_destroy(ce);
>>> + return;
>>> + }
>>> +
>>> deregister_context(ce, ce->guc_id.id, true);
>>> }
>>> @@ -1873,78 +1904,88 @@ static void __guc_context_destroy(struct intel_context *ce)
>>> }
>>> }
>>> +static void guc_flush_destroyed_contexts(struct intel_guc *guc)
>>> +{
>>> + struct intel_context *ce, *cn;
>>> + unsigned long flags;
>>> +
>>> + GEM_BUG_ON(!submission_disabled(guc) &&
>>> + guc_submission_initialized(guc));
>>> +
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> + list_for_each_entry_safe(ce, cn,
>>> + &guc->submission_state.destroyed_contexts,
>>> + destroyed_link) {
>>> + list_del_init(&ce->destroyed_link);
>>> + __release_guc_id(guc, ce);
>>> + __guc_context_destroy(ce);
>>> + }
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> +}
>>> +
>>> +static void deregister_destroyed_contexts(struct intel_guc *guc)
>>> +{
>>> + struct intel_context *ce, *cn;
>>> + unsigned long flags;
>>> +
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> + list_for_each_entry_safe(ce, cn,
>>> + &guc->submission_state.destroyed_contexts,
>>> + destroyed_link) {
>>> + list_del_init(&ce->destroyed_link);
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>
>> Lock drop and re-acquire is not safe - list_for_each_entry_safe only deal
>> with the list_del_init above. It does not help if someone else modifies the
>> list in the window while the lock is not held, in which case things will go
>> BOOM!
>>
>
> Good catch, but is this true? We always add via list_add_tail which if
> I'm reading the list_for_each_entry_safe macro correctly I think is safe
> to do as 'n = list_next_entry(n, member)' will just evaluate to the new
> tail on each iteration, right?
>
> Reference to macro below:
> #define list_for_each_entry_safe(pos, n, head, member) \
> for (pos = list_first_entry(head, typeof(*pos), member), \
> n = list_next_entry(pos, member); \
> &pos->member != (head); \
> pos = n, n = list_next_entry(n, member))
>
> Regardless probably safer to just not drop the lock.

Yes, otherwise a comment is needed to explain, but best to avoid such
smarts.

Or just use a different list if it fits better. As mentioned if it is a
very simple producer/consumer relationship which always unlinks all
items, and list head is not re-used for something else, then you can
consider llist_add/llist_del_all.

Regards,

Tvrtko

>
>> Not sure in what differnt ways you use this list, but perhaps you could
>> employ a lockless single linked list for this. In which case you could
>> atomically unlink all elements. Or just change this to not do lock dropping,
>> if you can safely use the same list_head to put on a local list or
>> something.
>>
>
> I think both options work - not sure why I drop the lock here. I'll play
> around with this and fix in the next rev.
>
> Matt
>
>> Regards,
>>
>> Tvrtko
>>
>>> + guc_lrc_desc_unpin(ce);
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> + }
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> +}
>>> +
>>> +static void destroyed_worker_func(struct work_struct *w)
>>> +{
>>> + struct intel_guc *guc = container_of(w, struct intel_guc,
>>> + submission_state.destroyed_worker);
>>> + struct intel_gt *gt = guc_to_gt(guc);
>>> + int tmp;
>>> +
>>> + with_intel_gt_pm(gt, tmp)
>>> + deregister_destroyed_contexts(guc);
>>> +}
>>> +
>>> static void guc_context_destroy(struct kref *kref)
>>> {
>>> struct intel_context *ce = container_of(kref, typeof(*ce), ref);
>>> - struct intel_runtime_pm *runtime_pm = ce->engine->uncore->rpm;
>>> struct intel_guc *guc = ce_to_guc(ce);
>>> - intel_wakeref_t wakeref;
>>> unsigned long flags;
>>> - bool disabled;
>>> + bool destroy;
>>> /*
>>> * If the guc_id is invalid this context has been stolen and we can free
>>> * it immediately. Also can be freed immediately if the context is not
>>> * registered with the GuC or the GuC is in the middle of a reset.
>>> */
>>> - if (context_guc_id_invalid(ce)) {
>>> - __guc_context_destroy(ce);
>>> - return;
>>> - } else if (submission_disabled(guc) ||
>>> - !lrc_desc_registered(guc, ce->guc_id.id)) {
>>> - release_guc_id(guc, ce);
>>> - __guc_context_destroy(ce);
>>> - return;
>>> - }
>>> -
>>> - /*
>>> - * We have to acquire the context spinlock and check guc_id again, if it
>>> - * is valid it hasn't been stolen and needs to be deregistered. We
>>> - * delete this context from the list of unpinned guc_id available to
>>> - * steal to seal a race with guc_lrc_desc_pin(). When the G2H CTB
>>> - * returns indicating this context has been deregistered the guc_id is
>>> - * returned to the pool of available guc_id.
>>> - */
>>> - spin_lock_irqsave(&guc->contexts_lock, flags);
>>> - if (context_guc_id_invalid(ce)) {
>>> - spin_unlock_irqrestore(&guc->contexts_lock, flags);
>>> - __guc_context_destroy(ce);
>>> - return;
>>> - }
>>> -
>>> - if (!list_empty(&ce->guc_id.link))
>>> - list_del_init(&ce->guc_id.link);
>>> - spin_unlock_irqrestore(&guc->contexts_lock, flags);
>>> -
>>> - /* Seal race with Reset */
>>> - spin_lock_irqsave(&ce->guc_state.lock, flags);
>>> - disabled = submission_disabled(guc);
>>> - if (likely(!disabled)) {
>>> - set_context_destroyed(ce);
>>> - clr_context_registered(ce);
>>> + spin_lock_irqsave(&guc->submission_state.lock, flags);
>>> + destroy = submission_disabled(guc) || context_guc_id_invalid(ce) ||
>>> + !lrc_desc_registered(guc, ce->guc_id.id);
>>> + if (likely(!destroy)) {
>>> + if (!list_empty(&ce->guc_id.link))
>>> + list_del_init(&ce->guc_id.link);
>>> + list_add_tail(&ce->destroyed_link,
>>> + &guc->submission_state.destroyed_contexts);
>>> + } else {
>>> + __release_guc_id(guc, ce);
>>> }
>>> - spin_unlock_irqrestore(&ce->guc_state.lock, flags);
>>> - if (unlikely(disabled)) {
>>> - release_guc_id(guc, ce);
>>> + spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>>> + if (unlikely(destroy)) {
>>> __guc_context_destroy(ce);
>>> return;
>>> }
>>> /*
>>> - * We defer GuC context deregistration until the context is destroyed
>>> - * in order to save on CTBs. With this optimization ideally we only need
>>> - * 1 CTB to register the context during the first pin and 1 CTB to
>>> - * deregister the context when the context is destroyed. Without this
>>> - * optimization, a CTB would be needed every pin & unpin.
>>> - *
>>> - * XXX: Need to acqiure the runtime wakeref as this can be triggered
>>> - * from context_free_worker when runtime wakeref is not held.
>>> - * guc_lrc_desc_unpin requires the runtime as a GuC register is written
>>> - * in H2G CTB to deregister the context. A future patch may defer this
>>> - * H2G CTB if the runtime wakeref is zero.
>>> + * We use a worker to issue the H2G to deregister the context as we can
>>> + * take the GT PM for the first time which isn't allowed from an atomic
>>> + * context.
>>> */
>>> - with_intel_runtime_pm(runtime_pm, wakeref)
>>> - guc_lrc_desc_unpin(ce);
>>> + queue_work(system_unbound_wq, &guc->submission_state.destroyed_worker);
>>> }
>>> static int guc_context_alloc(struct intel_context *ce)
>>> @@ -2703,8 +2744,8 @@ static bool __guc_submission_selected(struct intel_guc *guc)
>>> void intel_guc_submission_init_early(struct intel_guc *guc)
>>> {
>>> - guc->max_guc_ids = GUC_MAX_LRC_DESCRIPTORS;
>>> - guc->num_guc_ids = GUC_MAX_LRC_DESCRIPTORS;
>>> + guc->submission_state.max_guc_ids = GUC_MAX_LRC_DESCRIPTORS;
>>> + guc->submission_state.num_guc_ids = GUC_MAX_LRC_DESCRIPTORS;
>>> guc->submission_supported = __guc_submission_supported(guc);
>>> guc->submission_selected = __guc_submission_selected(guc);
>>> }
>>> @@ -2714,10 +2755,10 @@ g2h_context_lookup(struct intel_guc *guc, u32 desc_idx)
>>> {
>>> struct intel_context *ce;
>>> - if (unlikely(desc_idx >= guc->max_guc_ids)) {
>>> + if (unlikely(desc_idx >= guc->submission_state.max_guc_ids)) {
>>> drm_err(&guc_to_gt(guc)->i915->drm,
>>> "Invalid desc_idx %u, max %u",
>>> - desc_idx, guc->max_guc_ids);
>>> + desc_idx, guc->submission_state.max_guc_ids);
>>> return NULL;
>>> }
>>> @@ -2771,6 +2812,7 @@ int intel_guc_deregister_done_process_msg(struct intel_guc *guc,
>>> intel_context_put(ce);
>>> } else if (context_destroyed(ce)) {
>>> /* Context has been destroyed */
>>> + intel_gt_pm_put_async(guc_to_gt(guc));
>>> release_guc_id(guc, ce);
>>> __guc_context_destroy(ce);
>>> }
>>> @@ -3065,8 +3107,10 @@ void intel_guc_submission_print_info(struct intel_guc *guc,
>>> drm_printf(p, "GuC Number Outstanding Submission G2H: %u\n",
>>> atomic_read(&guc->outstanding_submission_g2h));
>>> - drm_printf(p, "GuC Number GuC IDs: %u\n", guc->num_guc_ids);
>>> - drm_printf(p, "GuC Max GuC IDs: %u\n", guc->max_guc_ids);
>>> + drm_printf(p, "GuC Number GuC IDs: %u\n",
>>> + guc->submission_state.num_guc_ids);
>>> + drm_printf(p, "GuC Max GuC IDs: %u\n",
>>> + guc->submission_state.max_guc_ids);
>>> drm_printf(p, "GuC tasklet count: %u\n\n",
>>> atomic_read(&sched_engine->tasklet.count));
>>>