NFS: Fix another nfs_wb_page() deadlock

J.R. Okajima reports that the call to sync_inode() in nfs_wb_page() can
deadlock with other writeback flush calls. It boils down to the fact
that we cannot ever call writeback_single_inode() while holding a page
lock (even if we do set nr_to_write to zero) since another process may
already be waiting in the call to do_writepages(), and so will deny us
the I_SYNC lock.

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

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b8a6d7af2a1..91679e2631e 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1518,14 +1518,17 @@ int nfs_wb_page(struct inode *inode, struct page *page)
         };
         int ret;
 
-        while(PagePrivate(page)) {
+        for (;;) {
                 wait_on_page_writeback(page);
                 if (clear_page_dirty_for_io(page)) {
                         ret = nfs_writepage_locked(page, &wbc);
                         if (ret < 0)
                                 goto out_error;
+                        continue;
                 }
-                ret = sync_inode(inode, &wbc);
+                if (!PagePrivate(page))
+                        break;
+                ret = nfs_commit_inode(inode, FLUSH_SYNC);
                 if (ret < 0)
                         goto out_error;
         }