NFS: Fix a race when doing NFS write coalescing

Currently we do write coalescing in a very inefficient manner: one pass in
generic_writepages() in order to lock the pages for writing, then one pass
in nfs_flush_mapping() and/or nfs_sync_mapping_wait() in order to gather
the locked pages for coalescing into RPC requests of size "wsize".

In fact, it turns out there is actually a deadlock possible here since we
only start I/O on the second pass. If the user signals the process while
we're in nfs_sync_mapping_wait(), for instance, then we may exit before
starting I/O on all the requests that have been queued up.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 3 insertions, 7 deletions

diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index b8b7bca3bac8..e556e57ef7ad 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -21,8 +21,7 @@
 /*
  * Valid flags for the radix tree
  */
-#define NFS_PAGE_TAG_DIRTY      0
-#define NFS_PAGE_TAG_WRITEBACK  1
+#define NFS_PAGE_TAG_WRITEBACK  0
 
 /*
  * Valid flags for a dirty buffer
@@ -72,9 +71,6 @@ extern	void nfs_clear_request(struct nfs_page *req);
 extern  void nfs_release_request(struct nfs_page *req);
 
 
-extern  long nfs_scan_dirty(struct address_space *mapping,
-                                struct writeback_control *wbc,
-                                struct list_head *dst);
 extern  int nfs_scan_list(struct nfs_inode *nfsi, struct list_head *head, struct list_head *dst,
                           unsigned long idx_start, unsigned int npages);
 extern  void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
@@ -84,8 +80,6 @@ extern	void nfs_pageio_init(struct nfs_pageio_descriptor *desc,
                              int how);
 extern  int nfs_pageio_add_request(struct nfs_pageio_descriptor *,
                                    struct nfs_page *);
-extern  void nfs_pageio_add_list(struct nfs_pageio_descriptor *,
-                                 struct list_head *);
 extern  void nfs_pageio_complete(struct nfs_pageio_descriptor *desc);
 extern  int nfs_wait_on_request(struct nfs_page *);
 extern  void nfs_unlock_request(struct nfs_page *req);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 0c78f7f4a976..daa6c125f66e 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -59,6 +59,8 @@ struct writeback_control {
         unsigned for_reclaim:1;         /* Invoked from the page allocator */
         unsigned for_writepages:1;      /* This is a writepages() call */
         unsigned range_cyclic:1;        /* range_start is cyclic */
+
+        void *fs_private;               /* For use by ->writepages() */
 };
 
 /*