AGP fix race condition between unmapping and freeing pages

With Andi's clflush fixup, we were getting hangs on server exit, flushing the
mappings after freeing each page helped.

This showed up a race condition where the pages after being freed could be
reused before the agp mappings had been flushed.  Flushing after each single
page is a bad thing for future drm work, so make the page destroy a two pass
unmapping all the pages, flushing the mappings, and then destroying the pages.

Signed-off-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
index 3db4f4076ed4..64b2f6d7059d 100644
--- a/drivers/char/agp/generic.c
+++ b/drivers/char/agp/generic.c
@@ -195,9 +195,12 @@ void agp_free_memory(struct agp_memory *curr)
 	}
 	if (curr->page_count != 0) {
 		for (i = 0; i < curr->page_count; i++) {
-			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]));
+			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_UNMAP);
 		}
 		flush_agp_mappings();
+		for (i = 0; i < curr->page_count; i++) {
+			curr->bridge->driver->agp_destroy_page(gart_to_virt(curr->memory[i]), AGP_PAGE_DESTROY_FREE);
+		}
 	}
 	agp_free_key(curr->key);
 	agp_free_page_array(curr);
@@ -1176,7 +1179,7 @@ void *agp_generic_alloc_page(struct agp_bridge_data *bridge)
 EXPORT_SYMBOL(agp_generic_alloc_page);
 
 
-void agp_generic_destroy_page(void *addr)
+void agp_generic_destroy_page(void *addr, int flags)
 {
 	struct page *page;
 
@@ -1184,10 +1187,14 @@ void agp_generic_destroy_page(void *addr)
 		return;
 
 	page = virt_to_page(addr);
-	unmap_page_from_agp(page);
-	put_page(page);
-	free_page((unsigned long)addr);
-	atomic_dec(&agp_bridge->current_memory_agp);
+	if (flags & AGP_PAGE_DESTROY_UNMAP)
+		unmap_page_from_agp(page);
+
+	if (flags & AGP_PAGE_DESTROY_FREE) {
+		put_page(page);
+		free_page((unsigned long)addr);
+		atomic_dec(&agp_bridge->current_memory_agp);
+	}
 }
 EXPORT_SYMBOL(agp_generic_destroy_page);