From 749310c372b2f6e5b5fed77602b3bad7f6551428 Mon Sep 17 00:00:00 2001 From: Timothy Strelchun Date: Sat, 19 Jun 2010 16:39:36 -0700 Subject: [PATCH 2/6] Fix various layer context lock related deadlock scenarios Changed dfb_layer_context_get_primary_region to return the error DFB_TEMPUNAVIL if the primary region is being destroyed. Previously in this scenario (which means the primary region's reference count was zero and there was not a request to create a new one), a deadlock could occur involving the layer context lock when the primary region was being destroyed by the main thread (single-app mode), the Fusion Loop thread (multi-app mode), or any other thread (such as linux_input thread that triggers the window stack input processing) is trying to get the primary region. In addition, object_reference_watcher would be called more than once when the reference count changes from 1 to 0 again in the implementation. --- src/core/layer_context.c | 22 ++++++++++++++++++++-- 1 files changed, 20 insertions(+), 2 deletions(-) diff --git a/src/core/layer_context.c b/src/core/layer_context.c index 757e7bd..f7dc939 100644 --- a/src/core/layer_context.c +++ b/src/core/layer_context.c @@ -470,6 +470,17 @@ dfb_layer_context_get_primary_region( CoreLayerContext *context, restart: while (context->primary.region) { + // Make sure the primary region's reference count is non-zero. If + // it is, a failure is returned to indicate that it is unavailable. + // In this scenario, this prevents the object_reference_watcher from + // being called more than once triggered by the reference count + // changing from 1 to 0 again. + int num = 0; + + if (dfb_layer_region_ref_stat( context->primary.region, &num ) || num == 0) { + dfb_layer_context_unlock( context ); + return DFB_TEMPUNAVAIL; + } /* Increase the primary region's reference counter. */ ret = dfb_layer_region_ref( context->primary.region ); if (ret == DFB_OK) @@ -478,6 +489,12 @@ restart: dfb_layer_context_unlock( context ); if (ret == DFB_LOCKED) { + // If the primary region is Fusion zero-locked (being destroyed) + // and creating a new primary region is not requested, return + // an error immediately. + if (!create) + return DFB_TEMPUNAVAIL; + //sched_yield(); usleep( 10000 ); @@ -729,8 +746,9 @@ dfb_layer_context_set_configuration( CoreLayerContext *context, /* Unlock the region surface */ if (region->surface) { if (D_FLAGS_IS_SET( region->state, CLRSF_REALIZED )) { - if (!D_FLAGS_IS_SET( region->state, CLRSF_FROZEN )) - D_ASSUME( region->surface_lock.buffer != NULL ); + // The region surface is now being left in an unlocked + // state, so the buffer (region->surface_lock.buffer) + // can be NULL even when not frozen. if (region->surface_lock.buffer) dfb_surface_unlock_buffer( region->surface, ®ion->surface_lock ); -- 1.6.1.9.g97c34