[patch 02/19] NFS: Fix a potential deadlock in nfs_release_page

[Greg KH]

-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Nikita Danilov <nikita@xxxxxxxxxxxxx>

nfs_wb_page() waits on request completion and, as a result, is not safe to be
called from nfs_release_page() invoked by VM scanner as part of GFP_NOFS
allocation. Fix possible deadlock by analyzing gfp mask and refusing to
release page if __GFP_FS is not set.

Signed-off-by: Nikita Danilov <danilov@xxxxxxxxx>
Signed-off-by: Trond Myklebust <Trond.Myklebust@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/nfs/file.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- linux-2.6.17.13.orig/fs/nfs/file.c
+++ linux-2.6.17.13/fs/nfs/file.c
@@ -325,7 +325,13 @@ static void nfs_invalidate_page(struct p
 
 static int nfs_release_page(struct page *page, gfp_t gfp)
 {
-	return !nfs_wb_page(page->mapping->host, page);
+	if (gfp & __GFP_FS)
+		return !nfs_wb_page(page->mapping->host, page);
+	else
+		/*
+		 * Avoid deadlock on nfs_wait_on_request().
+		 */
+		return 0;
 }
 
 struct address_space_operations nfs_file_aops = {

--
-
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