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>

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b8a6d7a..91679e2 100644 (file)
--- 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;
        }