From 3c3b177a9369b26890ced004867fb32708e8ef5b Mon Sep 17 00:00:00 2001 From: Maarten Lankhorst Date: Tue, 1 Jul 2014 12:58:00 +0200 Subject: reservation: add suppport for read-only access using rcu This adds some extra functions to deal with rcu. reservation_object_get_fences_rcu() will obtain the list of shared and exclusive fences without obtaining the ww_mutex. reservation_object_wait_timeout_rcu() will wait on all fences of the reservation_object, without obtaining the ww_mutex. reservation_object_test_signaled_rcu() will test if all fences of the reservation_object are signaled without using the ww_mutex. reservation_object_get_excl and reservation_object_get_list require the reservation object to be held, updating requires write_seqcount_begin/end. If only the exclusive fence is needed, rcu_dereference followed by fence_get_rcu can be used, if the shared fences are needed it's recommended to use the supplied functions. Signed-off-by: Maarten Lankhorst Acked-by: Sumit Semwal Acked-by: Daniel Vetter Reviewed-By: Thomas Hellstrom Signed-off-by: Greg Kroah-Hartman --- drivers/dma-buf/reservation.c | 336 ++++++++++++++++++++++++++++++++++++++---- 1 file changed, 310 insertions(+), 26 deletions(-) (limited to 'drivers/dma-buf/reservation.c') diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c index e6166723a9ae..3c97c8fa8d02 100644 --- a/drivers/dma-buf/reservation.c +++ b/drivers/dma-buf/reservation.c @@ -38,6 +38,11 @@ DEFINE_WW_CLASS(reservation_ww_class); EXPORT_SYMBOL(reservation_ww_class); +struct lock_class_key reservation_seqcount_class; +EXPORT_SYMBOL(reservation_seqcount_class); + +const char reservation_seqcount_string[] = "reservation_seqcount"; +EXPORT_SYMBOL(reservation_seqcount_string); /* * Reserve space to add a shared fence to a reservation_object, * must be called with obj->lock held. @@ -82,27 +87,37 @@ reservation_object_add_shared_inplace(struct reservation_object *obj, { u32 i; + fence_get(fence); + + preempt_disable(); + write_seqcount_begin(&obj->seq); + for (i = 0; i < fobj->shared_count; ++i) { - if (fobj->shared[i]->context == fence->context) { - struct fence *old_fence = fobj->shared[i]; + struct fence *old_fence; - fence_get(fence); + old_fence = rcu_dereference_protected(fobj->shared[i], + reservation_object_held(obj)); - fobj->shared[i] = fence; + if (old_fence->context == fence->context) { + /* memory barrier is added by write_seqcount_begin */ + RCU_INIT_POINTER(fobj->shared[i], fence); + write_seqcount_end(&obj->seq); + preempt_enable(); fence_put(old_fence); return; } } - fence_get(fence); - fobj->shared[fobj->shared_count] = fence; /* - * make the new fence visible before incrementing - * fobj->shared_count + * memory barrier is added by write_seqcount_begin, + * fobj->shared_count is protected by this lock too */ - smp_wmb(); + RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence); fobj->shared_count++; + + write_seqcount_end(&obj->seq); + preempt_enable(); } static void @@ -112,11 +127,12 @@ reservation_object_add_shared_replace(struct reservation_object *obj, struct fence *fence) { unsigned i; + struct fence *old_fence = NULL; fence_get(fence); if (!old) { - fobj->shared[0] = fence; + RCU_INIT_POINTER(fobj->shared[0], fence); fobj->shared_count = 1; goto done; } @@ -130,19 +146,38 @@ reservation_object_add_shared_replace(struct reservation_object *obj, fobj->shared_count = old->shared_count; for (i = 0; i < old->shared_count; ++i) { - if (fence && old->shared[i]->context == fence->context) { - fence_put(old->shared[i]); - fobj->shared[i] = fence; - fence = NULL; + struct fence *check; + + check = rcu_dereference_protected(old->shared[i], + reservation_object_held(obj)); + + if (!old_fence && check->context == fence->context) { + old_fence = check; + RCU_INIT_POINTER(fobj->shared[i], fence); } else - fobj->shared[i] = old->shared[i]; + RCU_INIT_POINTER(fobj->shared[i], check); + } + if (!old_fence) { + RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence); + fobj->shared_count++; } - if (fence) - fobj->shared[fobj->shared_count++] = fence; done: - obj->fence = fobj; - kfree(old); + preempt_disable(); + write_seqcount_begin(&obj->seq); + /* + * RCU_INIT_POINTER can be used here, + * seqcount provides the necessary barriers + */ + RCU_INIT_POINTER(obj->fence, fobj); + write_seqcount_end(&obj->seq); + preempt_enable(); + + if (old) + kfree_rcu(old, rcu); + + if (old_fence) + fence_put(old_fence); } /* @@ -158,7 +193,7 @@ void reservation_object_add_shared_fence(struct reservation_object *obj, obj->staged = NULL; if (!fobj) { - BUG_ON(old->shared_count == old->shared_max); + BUG_ON(old->shared_count >= old->shared_max); reservation_object_add_shared_inplace(obj, old, fence); } else reservation_object_add_shared_replace(obj, old, fobj, fence); @@ -168,26 +203,275 @@ EXPORT_SYMBOL(reservation_object_add_shared_fence); void reservation_object_add_excl_fence(struct reservation_object *obj, struct fence *fence) { - struct fence *old_fence = obj->fence_excl; + struct fence *old_fence = reservation_object_get_excl(obj); struct reservation_object_list *old; u32 i = 0; old = reservation_object_get_list(obj); - if (old) { + if (old) i = old->shared_count; - old->shared_count = 0; - } if (fence) fence_get(fence); - obj->fence_excl = fence; + preempt_disable(); + write_seqcount_begin(&obj->seq); + /* write_seqcount_begin provides the necessary memory barrier */ + RCU_INIT_POINTER(obj->fence_excl, fence); + if (old) + old->shared_count = 0; + write_seqcount_end(&obj->seq); + preempt_enable(); /* inplace update, no shared fences */ while (i--) - fence_put(old->shared[i]); + fence_put(rcu_dereference_protected(old->shared[i], + reservation_object_held(obj))); if (old_fence) fence_put(old_fence); } EXPORT_SYMBOL(reservation_object_add_excl_fence); + +int reservation_object_get_fences_rcu(struct reservation_object *obj, + struct fence **pfence_excl, + unsigned *pshared_count, + struct fence ***pshared) +{ + unsigned shared_count = 0; + unsigned retry = 1; + struct fence **shared = NULL, *fence_excl = NULL; + int ret = 0; + + while (retry) { + struct reservation_object_list *fobj; + unsigned seq; + + seq = read_seqcount_begin(&obj->seq); + + rcu_read_lock(); + + fobj = rcu_dereference(obj->fence); + if (fobj) { + struct fence **nshared; + size_t sz = sizeof(*shared) * fobj->shared_max; + + nshared = krealloc(shared, sz, + GFP_NOWAIT | __GFP_NOWARN); + if (!nshared) { + rcu_read_unlock(); + nshared = krealloc(shared, sz, GFP_KERNEL); + if (nshared) { + shared = nshared; + continue; + } + + ret = -ENOMEM; + shared_count = 0; + break; + } + shared = nshared; + memcpy(shared, fobj->shared, sz); + shared_count = fobj->shared_count; + } else + shared_count = 0; + fence_excl = rcu_dereference(obj->fence_excl); + + retry = read_seqcount_retry(&obj->seq, seq); + if (retry) + goto unlock; + + if (!fence_excl || fence_get_rcu(fence_excl)) { + unsigned i; + + for (i = 0; i < shared_count; ++i) { + if (fence_get_rcu(shared[i])) + continue; + + /* uh oh, refcount failed, abort and retry */ + while (i--) + fence_put(shared[i]); + + if (fence_excl) { + fence_put(fence_excl); + fence_excl = NULL; + } + + retry = 1; + break; + } + } else + retry = 1; + +unlock: + rcu_read_unlock(); + } + *pshared_count = shared_count; + if (shared_count) + *pshared = shared; + else { + *pshared = NULL; + kfree(shared); + } + *pfence_excl = fence_excl; + + return ret; +} +EXPORT_SYMBOL_GPL(reservation_object_get_fences_rcu); + +long reservation_object_wait_timeout_rcu(struct reservation_object *obj, + bool wait_all, bool intr, + unsigned long timeout) +{ + struct fence *fence; + unsigned seq, shared_count, i = 0; + long ret = timeout; + +retry: + fence = NULL; + shared_count = 0; + seq = read_seqcount_begin(&obj->seq); + rcu_read_lock(); + + if (wait_all) { + struct reservation_object_list *fobj = rcu_dereference(obj->fence); + + if (fobj) + shared_count = fobj->shared_count; + + if (read_seqcount_retry(&obj->seq, seq)) + goto unlock_retry; + + for (i = 0; i < shared_count; ++i) { + struct fence *lfence = rcu_dereference(fobj->shared[i]); + + if (test_bit(FENCE_FLAG_SIGNALED_BIT, &lfence->flags)) + continue; + + if (!fence_get_rcu(lfence)) + goto unlock_retry; + + if (fence_is_signaled(lfence)) { + fence_put(lfence); + continue; + } + + fence = lfence; + break; + } + } + + if (!shared_count) { + struct fence *fence_excl = rcu_dereference(obj->fence_excl); + + if (read_seqcount_retry(&obj->seq, seq)) + goto unlock_retry; + + if (fence_excl && + !test_bit(FENCE_FLAG_SIGNALED_BIT, &fence_excl->flags)) { + if (!fence_get_rcu(fence_excl)) + goto unlock_retry; + + if (fence_is_signaled(fence_excl)) + fence_put(fence_excl); + else + fence = fence_excl; + } + } + + rcu_read_unlock(); + if (fence) { + ret = fence_wait_timeout(fence, intr, ret); + fence_put(fence); + if (ret > 0 && wait_all && (i + 1 < shared_count)) + goto retry; + } + return ret; + +unlock_retry: + rcu_read_unlock(); + goto retry; +} +EXPORT_SYMBOL_GPL(reservation_object_wait_timeout_rcu); + + +static inline int +reservation_object_test_signaled_single(struct fence *passed_fence) +{ + struct fence *fence, *lfence = passed_fence; + int ret = 1; + + if (!test_bit(FENCE_FLAG_SIGNALED_BIT, &lfence->flags)) { + int ret; + + fence = fence_get_rcu(lfence); + if (!fence) + return -1; + + ret = !!fence_is_signaled(fence); + fence_put(fence); + } + return ret; +} + +bool reservation_object_test_signaled_rcu(struct reservation_object *obj, + bool test_all) +{ + unsigned seq, shared_count; + int ret = true; + +retry: + shared_count = 0; + seq = read_seqcount_begin(&obj->seq); + rcu_read_lock(); + + if (test_all) { + unsigned i; + + struct reservation_object_list *fobj = rcu_dereference(obj->fence); + + if (fobj) + shared_count = fobj->shared_count; + + if (read_seqcount_retry(&obj->seq, seq)) + goto unlock_retry; + + for (i = 0; i < shared_count; ++i) { + struct fence *fence = rcu_dereference(fobj->shared[i]); + + ret = reservation_object_test_signaled_single(fence); + if (ret < 0) + goto unlock_retry; + else if (!ret) + break; + } + + /* + * There could be a read_seqcount_retry here, but nothing cares + * about whether it's the old or newer fence pointers that are + * signaled. That race could still have happened after checking + * read_seqcount_retry. If you care, use ww_mutex_lock. + */ + } + + if (!shared_count) { + struct fence *fence_excl = rcu_dereference(obj->fence_excl); + + if (read_seqcount_retry(&obj->seq, seq)) + goto unlock_retry; + + if (fence_excl) { + ret = reservation_object_test_signaled_single(fence_excl); + if (ret < 0) + goto unlock_retry; + } + } + + rcu_read_unlock(); + return ret; + +unlock_retry: + rcu_read_unlock(); + goto retry; +} +EXPORT_SYMBOL_GPL(reservation_object_test_signaled_rcu); -- cgit