* Added a acquire_unreferenced_ref() to vm_store

* his has to be used by the page writer to make sure the vnode is still valid.
* This should have been the final nail on the Luposian bug - I haven't tested
  it yet, but we'll certainly see :-)


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@22462 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vm_types.h

@@ -219,19 +219,20 @@ struct vm_store {
 };
 
 typedef struct vm_store_ops {
-	void (*destroy)(struct vm_store *backing_store);
+	void (*destroy)(struct vm_store *backingStore);
-	status_t (*commit)(struct vm_store *backing_store, off_t size);
+	status_t (*commit)(struct vm_store *backingStore, off_t size);
-	bool (*has_page)(struct vm_store *backing_store, off_t offset);
+	bool (*has_page)(struct vm_store *backingStore, off_t offset);
-	status_t (*read)(struct vm_store *backing_store, off_t offset,
+	status_t (*read)(struct vm_store *backingStore, off_t offset,
 		const iovec *vecs, size_t count, size_t *_numBytes, bool mayBlock,
 		bool fsReenter);
-	status_t (*write)(struct vm_store *backing_store, off_t offset,
+	status_t (*write)(struct vm_store *backingStore, off_t offset,
 		const iovec *vecs, size_t count, size_t *_numBytes, bool mayBlock,
 		bool fsReenter);
-	status_t (*fault)(struct vm_store *backing_store,
+	status_t (*fault)(struct vm_store *backingStore,
 		struct vm_address_space *aspace, off_t offset);
-	void (*acquire_ref)(struct vm_store *backing_store);
+	status_t (*acquire_unreferenced_ref)(struct vm_store *backingStore);
-	void (*release_ref)(struct vm_store *backing_store);
+	void (*acquire_ref)(struct vm_store *backingStore);
+	void (*release_ref)(struct vm_store *backingStore);
 } vm_store_ops;
 
 #endif	/* _KERNEL_VM_TYPES_H */

src/system/kernel/cache/vnode_store.cpp

@@ -83,6 +83,15 @@ store_write(struct vm_store *_store, off_t offset, const iovec *vecs,
 }
 
 
+static status_t
+store_acquire_unreferenced_ref(struct vm_store *_store)
+{
+	vnode_store *store = (vnode_store *)_store;
+	struct vnode *vnode;
+	return vfs_get_vnode(store->device, store->inode, &vnode);
+}
+
+
 static void
 store_acquire_ref(struct vm_store *_store)
 {
@@ -106,6 +115,7 @@ static vm_store_ops sStoreOps = {
 	&store_read,
 	&store_write,
 	NULL,	/* fault */
+	&store_acquire_unreferenced_ref,
 	&store_acquire_ref,
 	&store_release_ref
 };
@@ -128,6 +138,7 @@ vm_create_vnode_store(struct vnode *vnode)
 	store->vnode = vnode;
 	store->file_cache_ref = NULL;
 
+	vfs_vnode_to_node_ref(vnode, &store->device, &store->inode);
 	return &store->vm;
 }
 

src/system/kernel/cache/vnode_store.h

@@ -12,6 +12,8 @@
 struct vnode_store {
 	vm_store		vm;
 	struct vnode*	vnode;
+	dev_t			device;
+	ino_t			inode;
 	void*			file_cache_ref;
 };
 

src/system/kernel/vm/vm_page.cpp

@@ -665,6 +665,15 @@ page_writer(void* /*unused*/)
 			if (!cacheLocker.IsLocked())
 				continue;
 
+			vm_cache *cache = page->cache;
+			if (cache->store->ops->acquire_unreferenced_ref != NULL) {
+				// we need our own reference to the store, as it might
+				// currently be destructed
+				if (cache->store->ops->acquire_unreferenced_ref(cache->store)
+						!= B_OK)
+					continue;
+			}
+
 			locker.Lock();
 			remove_page_from_queue(&sModifiedPageQueue, page);
 			page->state = PAGE_STATE_BUSY;
@@ -675,7 +684,7 @@ page_writer(void* /*unused*/)
 
 			//dprintf("write page %p, cache %p (%ld)\n", page, page->cache, page->cache->ref_count);
 			vm_clear_map_flags(page, PAGE_MODIFIED);
-			vm_cache_acquire_ref(page->cache);
+			vm_cache_acquire_ref(cache);
 			pages[numPages++] = page;
 		}
 
@@ -711,6 +720,8 @@ page_writer(void* /*unused*/)
 			busyConditions[i].Unpublish();
 
 			mutex_unlock(&cache->lock);
+			if (cache->store->ops->release_ref != NULL)
+				cache->store->ops->release_ref(cache->store);
 			vm_cache_release_ref(cache);
 		}
 	}

src/system/kernel/vm/vm_store_anonymous_noswap.cpp

@@ -154,6 +154,7 @@ static vm_store_ops anonymous_ops = {
 	&anonymous_read,
 	&anonymous_write,
 	&anonymous_fault,
+	NULL,		// acquire unreferenced ref
 	NULL,		// acquire ref
 	NULL		// release ref
 };

src/system/kernel/vm/vm_store_device.c

@@ -78,8 +78,9 @@ static vm_store_ops device_ops = {
 	&device_read,
 	&device_write,
 	&device_fault,
-	NULL,
+	NULL,		// acquire unreferenced ref
-	NULL
+	NULL,		// acquire ref
+	NULL		// release ref
 };
 
 

src/system/kernel/vm/vm_store_null.c

@@ -67,8 +67,9 @@ static vm_store_ops null_ops = {
 	&null_read,
 	&null_write,
 	&null_fault,
-	NULL,
+	NULL,		// acquire unreferenced ref
-	NULL
+	NULL,		// acquire ref
+	NULL		// release ref
 };