FS-Cache: Start processing an object's operations on that object's death

Start processing an object's operations when that object moves into the DYING
state as the object cannot be destroyed until all its outstanding operations
have completed.

Furthermore, make sure that read and allocation operations handle being woken
up on a dead object.  Such events are recorded in the Allocs.abt and
Retrvls.abt statistics as viewable through /proc/fs/fscache/stats.

The code for waiting for object activation for the read and allocation
operations is also extracted into its own function as it is much the same in
all cases, differing only in the stats incremented.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 55 insertions, 57 deletions

diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index fc76798..c598ea4 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -314,6 +314,43 @@ static int fscache_wait_for_deferred_lookup(struct fscache_cookie *cookie)
 }
 
 /*
+ * wait for an object to become active (or dead)
+ */
+static int fscache_wait_for_retrieval_activation(struct fscache_object *object,
+						 struct fscache_retrieval *op,
+						 atomic_t *stat_op_waits,
+						 atomic_t *stat_object_dead)
+{
+	int ret;
+
+	if (!test_bit(FSCACHE_OP_WAITING, &op->op.flags))
+		goto check_if_dead;
+
+	_debug(">>> WT");
+	fscache_stat(stat_op_waits);
+	if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
+			fscache_wait_bit_interruptible,
+			TASK_INTERRUPTIBLE) < 0) {
+		ret = fscache_cancel_op(&op->op);
+		if (ret == 0)
+			return -ERESTARTSYS;
+
+		/* it's been removed from the pending queue by another party,
+		 * so we should get to run shortly */
+		wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
+			    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
+	}
+	_debug("<<< GO");
+
+check_if_dead:
+	if (unlikely(fscache_object_is_dead(object))) {
+		fscache_stat(stat_object_dead);
+		return -ENOBUFS;
+	}
+	return 0;
+}
+
+/*
  * read a page from the cache or allocate a block in which to store it
  * - we return:
  *   -ENOMEM	- out of memory, nothing done
@@ -376,25 +413,12 @@ int __fscache_read_or_alloc_page(struct fscache_cookie *cookie,
 
 	/* we wait for the operation to become active, and then process it
 	 * *here*, in this thread, and not in the thread pool */
-	if (test_bit(FSCACHE_OP_WAITING, &op->op.flags)) {
-		_debug(">>> WT");
-		fscache_stat(&fscache_n_retrieval_op_waits);
-		if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
-				fscache_wait_bit_interruptible,
-				TASK_INTERRUPTIBLE) < 0) {
-			ret = fscache_cancel_op(&op->op);
-			if (ret == 0) {
-				ret = -ERESTARTSYS;
-				goto error;
-			}
-
-			/* it's been removed from the pending queue by another
-			 * party, so we should get to run shortly */
-			wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
-				    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
-		}
-		_debug("<<< GO");
-	}
+	ret = fscache_wait_for_retrieval_activation(
+		object, op,
+		__fscache_stat(&fscache_n_retrieval_op_waits),
+		__fscache_stat(&fscache_n_retrievals_object_dead));
+	if (ret < 0)
+		goto error;
 
 	/* ask the cache to honour the operation */
 	if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
@@ -506,25 +530,12 @@ int __fscache_read_or_alloc_pages(struct fscache_cookie *cookie,
 
 	/* we wait for the operation to become active, and then process it
 	 * *here*, in this thread, and not in the thread pool */
-	if (test_bit(FSCACHE_OP_WAITING, &op->op.flags)) {
-		_debug(">>> WT");
-		fscache_stat(&fscache_n_retrieval_op_waits);
-		if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
-				fscache_wait_bit_interruptible,
-				TASK_INTERRUPTIBLE) < 0) {
-			ret = fscache_cancel_op(&op->op);
-			if (ret == 0) {
-				ret = -ERESTARTSYS;
-				goto error;
-			}
-
-			/* it's been removed from the pending queue by another
-			 * party, so we should get to run shortly */
-			wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
-				    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
-		}
-		_debug("<<< GO");
-	}
+	ret = fscache_wait_for_retrieval_activation(
+		object, op,
+		__fscache_stat(&fscache_n_retrieval_op_waits),
+		__fscache_stat(&fscache_n_retrievals_object_dead));
+	if (ret < 0)
+		goto error;
 
 	/* ask the cache to honour the operation */
 	if (test_bit(FSCACHE_COOKIE_NO_DATA_YET, &object->cookie->flags)) {
@@ -612,25 +623,12 @@ int __fscache_alloc_page(struct fscache_cookie *cookie,
 
 	fscache_stat(&fscache_n_alloc_ops);
 
-	if (test_bit(FSCACHE_OP_WAITING, &op->op.flags)) {
-		_debug(">>> WT");
-		fscache_stat(&fscache_n_alloc_op_waits);
-		if (wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
-				fscache_wait_bit_interruptible,
-				TASK_INTERRUPTIBLE) < 0) {
-			ret = fscache_cancel_op(&op->op);
-			if (ret == 0) {
-				ret = -ERESTARTSYS;
-				goto error;
-			}
-
-			/* it's been removed from the pending queue by another
-			 * party, so we should get to run shortly */
-			wait_on_bit(&op->op.flags, FSCACHE_OP_WAITING,
-				    fscache_wait_bit, TASK_UNINTERRUPTIBLE);
-		}
-		_debug("<<< GO");
-	}
+	ret = fscache_wait_for_retrieval_activation(
+		object, op,
+		__fscache_stat(&fscache_n_alloc_op_waits),
+		__fscache_stat(&fscache_n_allocs_object_dead));
+	if (ret < 0)
+		goto error;
 
 	/* ask the cache to honour the operation */
 	fscache_stat(&fscache_n_cop_allocate_page);