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 maarten.lankhorst@canonical.com Reviewed-By: Thomas Hellstrom thellstrom@vmware.com --- drivers/dma-buf/dma-buf.c | 47 ++++-- drivers/dma-buf/fence.c | 2 drivers/dma-buf/reservation.c | 336 ++++++++++++++++++++++++++++++++++++++--- include/linux/fence.h | 17 ++ include/linux/reservation.h | 52 ++++-- 5 files changed, 400 insertions(+), 54 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index cb8379dfeed5..f3014c448e1e 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -137,7 +137,7 @@ static unsigned int dma_buf_poll(struct file *file, poll_table *poll) struct reservation_object_list *fobj; struct fence *fence_excl; unsigned long events; - unsigned shared_count; + unsigned shared_count, seq;
dmabuf = file->private_data; if (!dmabuf || !dmabuf->resv) @@ -151,14 +151,20 @@ static unsigned int dma_buf_poll(struct file *file, poll_table *poll) if (!events) return 0;
- ww_mutex_lock(&resv->lock, NULL); +retry: + seq = read_seqcount_begin(&resv->seq); + rcu_read_lock();
- fobj = resv->fence; - if (!fobj) - goto out; - - shared_count = fobj->shared_count; - fence_excl = resv->fence_excl; + fobj = rcu_dereference(resv->fence); + if (fobj) + shared_count = fobj->shared_count; + else + shared_count = 0; + fence_excl = rcu_dereference(resv->fence_excl); + if (read_seqcount_retry(&resv->seq, seq)) { + rcu_read_unlock(); + goto retry; + }
if (fence_excl && (!(events & POLLOUT) || shared_count == 0)) { struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl; @@ -176,14 +182,20 @@ static unsigned int dma_buf_poll(struct file *file, poll_table *poll) spin_unlock_irq(&dmabuf->poll.lock);
if (events & pevents) { - if (!fence_add_callback(fence_excl, &dcb->cb, + if (!fence_get_rcu(fence_excl)) { + /* force a recheck */ + events &= ~pevents; + dma_buf_poll_cb(NULL, &dcb->cb); + } else if (!fence_add_callback(fence_excl, &dcb->cb, dma_buf_poll_cb)) { events &= ~pevents; + fence_put(fence_excl); } else { /* * No callback queued, wake up any additional * waiters. */ + fence_put(fence_excl); dma_buf_poll_cb(NULL, &dcb->cb); } } @@ -205,13 +217,26 @@ static unsigned int dma_buf_poll(struct file *file, poll_table *poll) goto out;
for (i = 0; i < shared_count; ++i) { - struct fence *fence = fobj->shared[i]; + struct fence *fence = rcu_dereference(fobj->shared[i]);
+ if (!fence_get_rcu(fence)) { + /* + * fence refcount dropped to zero, this means + * that fobj has been freed + * + * call dma_buf_poll_cb and force a recheck! + */ + events &= ~POLLOUT; + dma_buf_poll_cb(NULL, &dcb->cb); + break; + } if (!fence_add_callback(fence, &dcb->cb, dma_buf_poll_cb)) { + fence_put(fence); events &= ~POLLOUT; break; } + fence_put(fence); }
/* No callback queued, wake up any additional waiters. */ @@ -220,7 +245,7 @@ static unsigned int dma_buf_poll(struct file *file, poll_table *poll) }
out: - ww_mutex_unlock(&resv->lock); + rcu_read_unlock(); return events; }
diff --git a/drivers/dma-buf/fence.c b/drivers/dma-buf/fence.c index 948bf00d955e..4222cb2aa96a 100644 --- a/drivers/dma-buf/fence.c +++ b/drivers/dma-buf/fence.c @@ -184,7 +184,7 @@ EXPORT_SYMBOL(fence_release);
void fence_free(struct fence *fence) { - kfree(fence); + kfree_rcu(fence, rcu); } EXPORT_SYMBOL(fence_free);
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); diff --git a/include/linux/fence.h b/include/linux/fence.h index b935cc650123..d174585b874b 100644 --- a/include/linux/fence.h +++ b/include/linux/fence.h @@ -28,6 +28,7 @@ #include <linux/kref.h> #include <linux/sched.h> #include <linux/printk.h> +#include <linux/rcupdate.h>
struct fence; struct fence_ops; @@ -37,6 +38,7 @@ struct fence_cb; * struct fence - software synchronization primitive * @refcount: refcount for this fence * @ops: fence_ops associated with this fence + * @rcu: used for releasing fence with kfree_rcu * @cb_list: list of all callbacks to call * @lock: spin_lock_irqsave used for locking * @context: execution context this fence belongs to, returned by @@ -70,6 +72,7 @@ struct fence_cb; struct fence { struct kref refcount; const struct fence_ops *ops; + struct rcu_head rcu; struct list_head cb_list; spinlock_t *lock; unsigned context, seqno; @@ -192,6 +195,20 @@ static inline struct fence *fence_get(struct fence *fence) }
/** + * fence_get_rcu - get a fence from a reservation_object_list with rcu read lock + * @fence: [in] fence to increase refcount of + * + * Function returns NULL if no refcount could be obtained, or the fence. + */ +static inline struct fence *fence_get_rcu(struct fence *fence) +{ + if (kref_get_unless_zero(&fence->refcount)) + return fence; + else + return NULL; +} + +/** * fence_put - decreases refcount of the fence * @fence: [in] fence to reduce refcount of */ diff --git a/include/linux/reservation.h b/include/linux/reservation.h index 2affe67dea6e..5a0b64cf68b4 100644 --- a/include/linux/reservation.h +++ b/include/linux/reservation.h @@ -42,22 +42,29 @@ #include <linux/ww_mutex.h> #include <linux/fence.h> #include <linux/slab.h> +#include <linux/seqlock.h> +#include <linux/rcupdate.h>
extern struct ww_class reservation_ww_class; +extern struct lock_class_key reservation_seqcount_class; +extern const char reservation_seqcount_string[];
struct reservation_object_list { + struct rcu_head rcu; u32 shared_count, shared_max; - struct fence *shared[]; + struct fence __rcu *shared[]; };
struct reservation_object { struct ww_mutex lock; + seqcount_t seq;
- struct fence *fence_excl; - struct reservation_object_list *fence; + struct fence __rcu *fence_excl; + struct reservation_object_list __rcu *fence; struct reservation_object_list *staged; };
+#define reservation_object_held(obj) lockdep_is_held(&(obj)->lock.base) #define reservation_object_assert_held(obj) \ lockdep_assert_held(&(obj)->lock.base)
@@ -66,8 +73,9 @@ reservation_object_init(struct reservation_object *obj) { ww_mutex_init(&obj->lock, &reservation_ww_class);
- obj->fence_excl = NULL; - obj->fence = NULL; + __seqcount_init(&obj->seq, reservation_seqcount_string, &reservation_seqcount_class); + RCU_INIT_POINTER(obj->fence, NULL); + RCU_INIT_POINTER(obj->fence_excl, NULL); obj->staged = NULL; }
@@ -76,18 +84,20 @@ reservation_object_fini(struct reservation_object *obj) { int i; struct reservation_object_list *fobj; + struct fence *excl;
/* * This object should be dead and all references must have - * been released to it. + * been released to it, so no need to be protected with rcu. */ - if (obj->fence_excl) - fence_put(obj->fence_excl); + excl = rcu_dereference_protected(obj->fence_excl, 1); + if (excl) + fence_put(excl);
- fobj = obj->fence; + fobj = rcu_dereference_protected(obj->fence, 1); if (fobj) { for (i = 0; i < fobj->shared_count; ++i) - fence_put(fobj->shared[i]); + fence_put(rcu_dereference_protected(fobj->shared[i], 1));
kfree(fobj); } @@ -99,17 +109,15 @@ reservation_object_fini(struct reservation_object *obj) static inline struct reservation_object_list * reservation_object_get_list(struct reservation_object *obj) { - reservation_object_assert_held(obj); - - return obj->fence; + return rcu_dereference_protected(obj->fence, + reservation_object_held(obj)); }
static inline struct fence * reservation_object_get_excl(struct reservation_object *obj) { - reservation_object_assert_held(obj); - - return obj->fence_excl; + return rcu_dereference_protected(obj->fence_excl, + reservation_object_held(obj)); }
int reservation_object_reserve_shared(struct reservation_object *obj); @@ -119,4 +127,16 @@ void reservation_object_add_shared_fence(struct reservation_object *obj, void reservation_object_add_excl_fence(struct reservation_object *obj, struct fence *fence);
+int reservation_object_get_fences_rcu(struct reservation_object *obj, + struct fence **pfence_excl, + unsigned *pshared_count, + struct fence ***pshared); + +long reservation_object_wait_timeout_rcu(struct reservation_object *obj, + bool wait_all, bool intr, + unsigned long timeout); + +bool reservation_object_test_signaled_rcu(struct reservation_object *obj, + bool test_all); + #endif /* _LINUX_RESERVATION_H */