NFS: Clean up nfs_lock_and_join_requests()

Clean up nfs_lock_and_join_requests() to simplify the calculation
of the range covered by the page group, taking into account the
presence of mirrors.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/pagelist.c

@@ -130,6 +130,80 @@ nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
 }
 EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);
 
+/*
+ * nfs_unroll_locks -  unlock all newly locked reqs and wait on @req
+ * @head: head request of page group, must be holding head lock
+ * @req: request that couldn't lock and needs to wait on the req bit lock
+ *
+ * This is a helper function for nfs_lock_and_join_requests
+ * returns 0 on success, < 0 on error.
+ */
+static void
+nfs_unroll_locks(struct nfs_page *head, struct nfs_page *req)
+{
+	struct nfs_page *tmp;
+
+	/* relinquish all the locks successfully grabbed this run */
+	for (tmp = head->wb_this_page ; tmp != req; tmp = tmp->wb_this_page) {
+		if (!kref_read(&tmp->wb_kref))
+			continue;
+		nfs_unlock_and_release_request(tmp);
+	}
+}
+
+/*
+ * nfs_page_group_lock_subreq -  try to lock a subrequest
+ * @head: head request of page group
+ * @subreq: request to lock
+ *
+ * This is a helper function for nfs_lock_and_join_requests which
+ * must be called with the head request and page group both locked.
+ * On error, it returns with the page group unlocked.
+ */
+static int
+nfs_page_group_lock_subreq(struct nfs_page *head, struct nfs_page *subreq)
+{
+	int ret;
+
+	if (!kref_get_unless_zero(&subreq->wb_kref))
+		return 0;
+	while (!nfs_lock_request(subreq)) {
+		nfs_page_group_unlock(head);
+		ret = nfs_wait_on_request(subreq);
+		if (!ret)
+			ret = nfs_page_group_lock(head);
+		if (ret < 0) {
+			nfs_unroll_locks(head, subreq);
+			nfs_release_request(subreq);
+			return ret;
+		}
+	}
+	return 0;
+}
+
+/*
+ * nfs_page_group_lock_subrequests -  try to lock the subrequests
+ * @head: head request of page group
+ *
+ * This is a helper function for nfs_lock_and_join_requests which
+ * must be called with the head request and page group both locked.
+ * On error, it returns with the page group unlocked.
+ */
+int nfs_page_group_lock_subrequests(struct nfs_page *head)
+{
+	struct nfs_page *subreq;
+	int ret;
+
+	/* lock each request in the page group */
+	for (subreq = head->wb_this_page; subreq != head;
+			subreq = subreq->wb_this_page) {
+		ret = nfs_page_group_lock_subreq(head, subreq);
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
 /*
  * nfs_page_set_headlock - set the request PG_HEADLOCK
  * @req: request that is to be locked

fs/nfs/write.c

@@ -379,34 +379,6 @@ static void nfs_end_page_writeback(struct nfs_page *req)
 		clear_bdi_congested(inode_to_bdi(inode), BLK_RW_ASYNC);
 }
 
-/*
- * nfs_unroll_locks_and_wait -  unlock all newly locked reqs and wait on @req
- *
- * this is a helper function for nfs_lock_and_join_requests
- *
- * @inode - inode associated with request page group, must be holding inode lock
- * @head  - head request of page group, must be holding head lock
- * @req   - request that couldn't lock and needs to wait on the req bit lock
- *
- * NOTE: this must be called holding page_group bit lock
- *       which will be released before returning.
- *
- * returns 0 on success, < 0 on error.
- */
-static void
-nfs_unroll_locks(struct inode *inode, struct nfs_page *head,
-			  struct nfs_page *req)
-{
-	struct nfs_page *tmp;
-
-	/* relinquish all the locks successfully grabbed this run */
-	for (tmp = head->wb_this_page ; tmp != req; tmp = tmp->wb_this_page) {
-		if (!kref_read(&tmp->wb_kref))
-			continue;
-		nfs_unlock_and_release_request(tmp);
-	}
-}
-
 /*
  * nfs_destroy_unlinked_subrequests - destroy recently unlinked subrequests
  *
@@ -487,7 +459,7 @@ nfs_lock_and_join_requests(struct page *page)
 	struct inode *inode = page_file_mapping(page)->host;
 	struct nfs_page *head, *subreq;
 	struct nfs_page *destroy_list = NULL;
-	unsigned int total_bytes;
+	unsigned int pgbase, off, bytes;
 	int ret;
 
 try_again:
@@ -520,49 +492,30 @@ nfs_lock_and_join_requests(struct page *page)
 		goto release_request;
 
 	/* lock each request in the page group */
-	total_bytes = head->wb_bytes;
+	ret = nfs_page_group_lock_subrequests(head);
+	if (ret < 0)
+		goto release_request;
+
+	pgbase = head->wb_pgbase;
+	bytes = head->wb_bytes;
+	off = head->wb_offset;
 	for (subreq = head->wb_this_page; subreq != head;
 			subreq = subreq->wb_this_page) {
-
-		if (!kref_get_unless_zero(&subreq->wb_kref)) {
-			if (subreq->wb_offset == head->wb_offset + total_bytes)
-				total_bytes += subreq->wb_bytes;
-			continue;
-		}
-
-		while (!nfs_lock_request(subreq)) {
-			/*
-			 * Unlock page to allow nfs_page_group_sync_on_bit()
-			 * to succeed
-			 */
-			nfs_page_group_unlock(head);
-			ret = nfs_wait_on_request(subreq);
-			if (!ret)
-				ret = nfs_page_group_lock(head);
-			if (ret < 0) {
-				nfs_unroll_locks(inode, head, subreq);
-				nfs_release_request(subreq);
-				goto release_request;
-			}
-		}
-		/*
-		 * Subrequests are always contiguous, non overlapping
-		 * and in order - but may be repeated (mirrored writes).
-		 */
-		if (subreq->wb_offset == (head->wb_offset + total_bytes)) {
-			/* keep track of how many bytes this group covers */
-			total_bytes += subreq->wb_bytes;
-		} else if (WARN_ON_ONCE(subreq->wb_offset < head->wb_offset ||
-			    ((subreq->wb_offset + subreq->wb_bytes) >
-			     (head->wb_offset + total_bytes)))) {
-			nfs_page_group_unlock(head);
-			nfs_unroll_locks(inode, head, subreq);
-			nfs_unlock_and_release_request(subreq);
-			ret = -EIO;
-			goto release_request;
+		/* Subrequests should always form a contiguous range */
+		if (pgbase > subreq->wb_pgbase) {
+			off -= pgbase - subreq->wb_pgbase;
+			bytes += pgbase - subreq->wb_pgbase;
+			pgbase = subreq->wb_pgbase;
 		}
+		bytes = max(subreq->wb_pgbase + subreq->wb_bytes
+				- pgbase, bytes);
 	}
 
+	/* Set the head request's range to cover the former page group */
+	head->wb_pgbase = pgbase;
+	head->wb_bytes = bytes;
+	head->wb_offset = off;
+
 	/* Now that all requests are locked, make sure they aren't on any list.
 	 * Commit list removal accounting is done after locks are dropped */
 	subreq = head;
@@ -576,10 +529,6 @@ nfs_lock_and_join_requests(struct page *page)
 		/* destroy list will be terminated by head */
 		destroy_list = head->wb_this_page;
 		head->wb_this_page = head;
-
-		/* change head request to cover whole range that
-		 * the former page group covered */
-		head->wb_bytes = total_bytes;
 	}
 
 	/* Postpone destruction of this request */

include/linux/nfs_page.h

@@ -139,6 +139,7 @@ extern size_t nfs_generic_pg_test(struct nfs_pageio_descriptor *desc,
 extern  int nfs_wait_on_request(struct nfs_page *);
 extern	void nfs_unlock_request(struct nfs_page *req);
 extern	void nfs_unlock_and_release_request(struct nfs_page *);
+extern	int nfs_page_group_lock_subrequests(struct nfs_page *head);
 extern int nfs_page_group_lock(struct nfs_page *);
 extern void nfs_page_group_unlock(struct nfs_page *);
 extern bool nfs_page_group_sync_on_bit(struct nfs_page *, unsigned int);