3 files changed, 25 insertions, 2 deletions

diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index cbdd1c6aaa94..c5bb51a29e80 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -355,6 +355,26 @@ void nfs_pageio_complete(struct nfs_pageio_descriptor *desc)
         nfs_pageio_doio(desc);
 }
 
+/**
+ * nfs_pageio_cond_complete - Conditional I/O completion
+ * @desc: pointer to io descriptor
+ * @index: page index
+ *
+ * It is important to ensure that processes don't try to take locks
+ * on non-contiguous ranges of pages as that might deadlock. This
+ * function should be called before attempting to wait on a locked
+ * nfs_page. It will complete the I/O if the page index 'index'
+ * is not contiguous with the existing list of pages in 'desc'.
+ */
+void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *desc, pgoff_t index)
+{
+        if (!list_empty(&desc->pg_list)) {
+                struct nfs_page *prev = nfs_list_entry(desc->pg_list.prev);
+                if (index != prev->wb_index + 1)
+                        nfs_pageio_doio(desc);
+        }
+}
+
 #define NFS_SCAN_MAXENTRIES 16
 /**
  * nfs_scan_list - Scan a list for matching requests
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b084c03ce493..af344a158e01 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -273,8 +273,6 @@ static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
                  *       request as dirty (in which case we don't care).
                  */
                 spin_unlock(req_lock);
-                /* Prevent deadlock! */
-                nfs_pageio_complete(pgio);
                 ret = nfs_wait_on_request(req);
                 nfs_release_request(req);
                 if (ret != 0)
@@ -321,6 +319,8 @@ static int nfs_writepage_locked(struct page *page, struct writeback_control *wbc
                 pgio = &mypgio;
         }
 
+        nfs_pageio_cond_complete(pgio, page->index);
+
         err = nfs_page_async_flush(pgio, page);
         if (err <= 0)
                 goto out;
@@ -329,6 +329,8 @@ static int nfs_writepage_locked(struct page *page, struct writeback_control *wbc
         if (!offset)
                 goto out;
 
+        nfs_pageio_cond_complete(pgio, page->index);
+
         ctx = nfs_find_open_context(inode, NULL, FMODE_WRITE);
         if (ctx == NULL) {
                 err = -EBADF;
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index 41afab6b5f09..bd193af80162 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -81,6 +81,7 @@ extern	void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
 extern  int nfs_pageio_add_request(struct nfs_pageio_descriptor *,
                                    struct nfs_page *);
 extern  void nfs_pageio_complete(struct nfs_pageio_descriptor *desc);
+extern  void nfs_pageio_cond_complete(struct nfs_pageio_descriptor *, pgoff_t);
 extern  int nfs_wait_on_request(struct nfs_page *);
 extern  void nfs_unlock_request(struct nfs_page *req);
 extern  int nfs_set_page_writeback_locked(struct nfs_page *req);