diff options
| -rw-r--r-- | drivers/dma-buf/dma-fence.c | 111 | ||||
| -rw-r--r-- | include/linux/dma-fence.h | 31 | ||||
| -rw-r--r-- | include/trace/events/dma_fence.h | 38 |
3 files changed, 157 insertions, 23 deletions
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 74f9e4b665e3..3f78c56b58dc 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -511,12 +511,20 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout) dma_fence_enable_sw_signaling(fence); - trace_dma_fence_wait_start(fence); + if (trace_dma_fence_wait_start_enabled()) { + rcu_read_lock(); + trace_dma_fence_wait_start(fence); + rcu_read_unlock(); + } if (fence->ops->wait) ret = fence->ops->wait(fence, intr, timeout); else ret = dma_fence_default_wait(fence, intr, timeout); - trace_dma_fence_wait_end(fence); + if (trace_dma_fence_wait_end_enabled()) { + rcu_read_lock(); + trace_dma_fence_wait_end(fence); + rcu_read_unlock(); + } return ret; } EXPORT_SYMBOL(dma_fence_wait_timeout); @@ -533,16 +541,23 @@ void dma_fence_release(struct kref *kref) struct dma_fence *fence = container_of(kref, struct dma_fence, refcount); + rcu_read_lock(); trace_dma_fence_destroy(fence); - if (WARN(!list_empty(&fence->cb_list) && - !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags), - "Fence %s:%s:%llx:%llx released with pending signals!\n", - dma_fence_driver_name(fence), - dma_fence_timeline_name(fence), - fence->context, fence->seqno)) { + if (!list_empty(&fence->cb_list) && + !test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) { + const char __rcu *timeline; + const char __rcu *driver; unsigned long flags; + driver = dma_fence_driver_name(fence); + timeline = dma_fence_timeline_name(fence); + + WARN(1, + "Fence %s:%s:%llx:%llx released with pending signals!\n", + rcu_dereference(driver), rcu_dereference(timeline), + fence->context, fence->seqno); + /* * Failed to signal before release, likely a refcounting issue. * @@ -556,6 +571,8 @@ void dma_fence_release(struct kref *kref) spin_unlock_irqrestore(fence->lock, flags); } + rcu_read_unlock(); + if (fence->ops->release) fence->ops->release(fence); else @@ -982,11 +999,21 @@ EXPORT_SYMBOL(dma_fence_set_deadline); */ void dma_fence_describe(struct dma_fence *fence, struct seq_file *seq) { + const char __rcu *timeline; + const char __rcu *driver; + + rcu_read_lock(); + + timeline = dma_fence_timeline_name(fence); + driver = dma_fence_driver_name(fence); + seq_printf(seq, "%s %s seq %llu %ssignalled\n", - dma_fence_driver_name(fence), - dma_fence_timeline_name(fence), + rcu_dereference(driver), + rcu_dereference(timeline), fence->seqno, dma_fence_is_signaled(fence) ? "" : "un"); + + rcu_read_unlock(); } EXPORT_SYMBOL(dma_fence_describe); @@ -1055,3 +1082,67 @@ dma_fence_init64(struct dma_fence *fence, const struct dma_fence_ops *ops, BIT(DMA_FENCE_FLAG_SEQNO64_BIT)); } EXPORT_SYMBOL(dma_fence_init64); + +/** + * dma_fence_driver_name - Access the driver name + * @fence: the fence to query + * + * Returns a driver name backing the dma-fence implementation. + * + * IMPORTANT CONSIDERATION: + * Dma-fence contract stipulates that access to driver provided data (data not + * directly embedded into the object itself), such as the &dma_fence.lock and + * memory potentially accessed by the &dma_fence.ops functions, is forbidden + * after the fence has been signalled. Drivers are allowed to free that data, + * and some do. + * + * To allow safe access drivers are mandated to guarantee a RCU grace period + * between signalling the fence and freeing said data. + * + * As such access to the driver name is only valid inside a RCU locked section. + * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded + * by the &rcu_read_lock and &rcu_read_unlock pair. + */ +const char __rcu *dma_fence_driver_name(struct dma_fence *fence) +{ + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), + "RCU protection is required for safe access to returned string"); + + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) + return fence->ops->get_driver_name(fence); + else + return "detached-driver"; +} +EXPORT_SYMBOL(dma_fence_driver_name); + +/** + * dma_fence_timeline_name - Access the timeline name + * @fence: the fence to query + * + * Returns a timeline name provided by the dma-fence implementation. + * + * IMPORTANT CONSIDERATION: + * Dma-fence contract stipulates that access to driver provided data (data not + * directly embedded into the object itself), such as the &dma_fence.lock and + * memory potentially accessed by the &dma_fence.ops functions, is forbidden + * after the fence has been signalled. Drivers are allowed to free that data, + * and some do. + * + * To allow safe access drivers are mandated to guarantee a RCU grace period + * between signalling the fence and freeing said data. + * + * As such access to the driver name is only valid inside a RCU locked section. + * The pointer MUST be both queried and USED ONLY WITHIN a SINGLE block guarded + * by the &rcu_read_lock and &rcu_read_unlock pair. + */ +const char __rcu *dma_fence_timeline_name(struct dma_fence *fence) +{ + RCU_LOCKDEP_WARN(!rcu_read_lock_held(), + "RCU protection is required for safe access to returned string"); + + if (!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) + return fence->ops->get_driver_name(fence); + else + return "signaled-timeline"; +} +EXPORT_SYMBOL(dma_fence_timeline_name); diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index 10a849cb2d3f..64639e104110 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -378,15 +378,28 @@ bool dma_fence_remove_callback(struct dma_fence *fence, struct dma_fence_cb *cb); void dma_fence_enable_sw_signaling(struct dma_fence *fence); -static inline const char *dma_fence_driver_name(struct dma_fence *fence) -{ - return fence->ops->get_driver_name(fence); -} - -static inline const char *dma_fence_timeline_name(struct dma_fence *fence) -{ - return fence->ops->get_timeline_name(fence); -} +/** + * DOC: Safe external access to driver provided object members + * + * All data not stored directly in the dma-fence object, such as the + * &dma_fence.lock and memory potentially accessed by functions in the + * &dma_fence.ops table, MUST NOT be accessed after the fence has been signalled + * because after that point drivers are allowed to free it. + * + * All code accessing that data via the dma-fence API (or directly, which is + * discouraged), MUST make sure to contain the complete access within a + * &rcu_read_lock and &rcu_read_unlock pair. + * + * Some dma-fence API handles this automatically, while other, as for example + * &dma_fence_driver_name and &dma_fence_timeline_name, leave that + * responsibility to the caller. + * + * To enable this scheme to work drivers MUST ensure a RCU grace period elapses + * between signalling the fence and freeing the said data. + * + */ +const char __rcu *dma_fence_driver_name(struct dma_fence *fence); +const char __rcu *dma_fence_timeline_name(struct dma_fence *fence); /** * dma_fence_is_signaled_locked - Return an indication if the fence diff --git a/include/trace/events/dma_fence.h b/include/trace/events/dma_fence.h index 84c83074ee81..4814a65b68dc 100644 --- a/include/trace/events/dma_fence.h +++ b/include/trace/events/dma_fence.h @@ -34,14 +34,44 @@ DECLARE_EVENT_CLASS(dma_fence, __entry->seqno) ); -DEFINE_EVENT(dma_fence, dma_fence_emit, +/* + * Safe only for call sites which are guaranteed to not race with fence + * signaling,holding the fence->lock and having checked for not signaled, or the + * signaling path itself. + */ +DECLARE_EVENT_CLASS(dma_fence_unsignaled, + + TP_PROTO(struct dma_fence *fence), + + TP_ARGS(fence), + + TP_STRUCT__entry( + __string(driver, fence->ops->get_driver_name(fence)) + __string(timeline, fence->ops->get_timeline_name(fence)) + __field(unsigned int, context) + __field(unsigned int, seqno) + ), + + TP_fast_assign( + __assign_str(driver); + __assign_str(timeline); + __entry->context = fence->context; + __entry->seqno = fence->seqno; + ), + + TP_printk("driver=%s timeline=%s context=%u seqno=%u", + __get_str(driver), __get_str(timeline), __entry->context, + __entry->seqno) +); + +DEFINE_EVENT(dma_fence_unsignaled, dma_fence_emit, TP_PROTO(struct dma_fence *fence), TP_ARGS(fence) ); -DEFINE_EVENT(dma_fence, dma_fence_init, +DEFINE_EVENT(dma_fence_unsignaled, dma_fence_init, TP_PROTO(struct dma_fence *fence), @@ -55,14 +85,14 @@ DEFINE_EVENT(dma_fence, dma_fence_destroy, TP_ARGS(fence) ); -DEFINE_EVENT(dma_fence, dma_fence_enable_signal, +DEFINE_EVENT(dma_fence_unsignaled, dma_fence_enable_signal, TP_PROTO(struct dma_fence *fence), TP_ARGS(fence) ); -DEFINE_EVENT(dma_fence, dma_fence_signaled, +DEFINE_EVENT(dma_fence_unsignaled, dma_fence_signaled, TP_PROTO(struct dma_fence *fence), |