NFS: Add an iocounter wait function for async RPC tasks

By sleeping on a new NFS Unlock-On-Close waitqueue, rpc tasks may wait for
a lock context's iocounter to reach zero.  The rpc waitqueue is only woken
when the open_context has the NFS_CONTEXT_UNLOCK flag set in order to
mitigate spurious wake-ups for any iocounter reaching zero.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

5 files changed, 37 insertions, 1 deletions

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 3ffbffe8f39f..3e7b2e6a7cfb 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -218,6 +218,7 @@ static void nfs_cb_idr_remove_locked(struct nfs_client *clp)
 static void pnfs_init_server(struct nfs_server *server)
 {
         rpc_init_wait_queue(&server->roc_rpcwaitq, "pNFS ROC");
+        rpc_init_wait_queue(&server->uoc_rpcwaitq, "NFS UOC");
 }
 
 #else
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index f53610672f03..ad92b401326c 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -102,6 +102,35 @@ nfs_iocounter_wait(struct nfs_lock_context *l_ctx)
                         TASK_KILLABLE);
 }
 
+/**
+ * nfs_async_iocounter_wait - wait on a rpc_waitqueue for I/O
+ * to complete
+ * @task: the rpc_task that should wait
+ * @l_ctx: nfs_lock_context with io_counter to check
+ *
+ * Returns true if there is outstanding I/O to wait on and the
+ * task has been put to sleep.
+ */
+bool
+nfs_async_iocounter_wait(struct rpc_task *task, struct nfs_lock_context *l_ctx)
+{
+        struct inode *inode = d_inode(l_ctx->open_context->dentry);
+        bool ret = false;
+
+        if (atomic_read(&l_ctx->io_count) > 0) {
+                rpc_sleep_on(&NFS_SERVER(inode)->uoc_rpcwaitq, task, NULL);
+                ret = true;
+        }
+
+        if (atomic_read(&l_ctx->io_count) == 0) {
+                rpc_wake_up_queued_task(&NFS_SERVER(inode)->uoc_rpcwaitq, task);
+                ret = false;
+        }
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(nfs_async_iocounter_wait);
+
 /*
  * nfs_page_group_lock - lock the head of the page group
  * @req - request in group that is to be locked
@@ -385,8 +414,11 @@ static void nfs_clear_request(struct nfs_page *req)
                 req->wb_page = NULL;
         }
         if (l_ctx != NULL) {
-                if (atomic_dec_and_test(&l_ctx->io_count))
+                if (atomic_dec_and_test(&l_ctx->io_count)) {
                         wake_up_atomic_t(&l_ctx->io_count);
+                        if (test_bit(NFS_CONTEXT_UNLOCK, &ctx->flags))
+                                rpc_wake_up(&NFS_SERVER(d_inode(ctx->dentry))->uoc_rpcwaitq);
+                }
                 nfs_put_lock_context(l_ctx);
                 req->wb_lock_context = NULL;
         }
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 1b29915247b2..9aa044e76820 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -76,6 +76,7 @@ struct nfs_open_context {
 #define NFS_CONTEXT_ERROR_WRITE         (0)
 #define NFS_CONTEXT_RESEND_WRITES       (1)
 #define NFS_CONTEXT_BAD                 (2)
+#define NFS_CONTEXT_UNLOCK      (3)
         int error;
 
         struct list_head list;
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index b34097c67848..2a70f34dffe8 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -222,6 +222,7 @@ struct nfs_server {
         u32                     mountd_version;
         unsigned short          mountd_port;
         unsigned short          mountd_protocol;
+        struct rpc_wait_queue   uoc_rpcwaitq;
 };
 
 /* Server capabilities */
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index 6f01e28bba27..247cc3d3498f 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -141,6 +141,7 @@ extern int nfs_page_group_lock(struct nfs_page *, bool);
 extern void nfs_page_group_lock_wait(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);
+extern bool nfs_async_iocounter_wait(struct rpc_task *, struct nfs_lock_context *);
 
 /*
  * Lock the page of an asynchronous request