Patch "mm: silently skip readahead for DAX inodes" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

mm: silently skip readahead for DAX inodes

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-silently-skip-readahead-for-dax-inodes.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ross Zwisler <[email protected]>
Date: Thu, 25 Aug 2016 15:17:17 -0700
Subject: mm: silently skip readahead for DAX inodes

From: Ross Zwisler <[email protected]>

commit 11bd969fdefea3ac0cb9791224f1e09784e21e58 upstream.

For DAX inodes we need to be careful to never have page cache pages in the mapping->page_tree. This radix tree should be composed only of DAX exceptional entries and zero pages.

ltp's readahead02 test was triggering a warning because we were trying to insert a DAX exceptional entry but found that a page cache page had already been inserted into the tree. This page was being inserted into the radix tree in response to a readahead(2) call.

Readahead doesn't make sense for DAX inodes, but we don't want it to report a failure either. Instead, we just return success and don't do any work.

---
 mm/readahead.c |    9 +++++++++
 1 file changed, 9 insertions(+)

@@ -8,6 +8,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/dax.h>
 #include <linux/gfp.h>
 #include <linux/export.h>
 #include <linux/blkdev.h>

@@ -545,6 +546,14 @@ do_readahead(struct address_space *mappi
 	if (!mapping || !mapping->a_ops)
 		return -EINVAL;
 
+	/*
+	 * Readahead doesn't make sense for DAX inodes, but we don't want it
+	 * to report a failure either.  Instead, we just return success and
+	 * don't do any work.
+	 */
+	if (dax_mapping(mapping))
+		return 0;
+
 	return force_page_cache_readahead(mapping, filp, index, nr);
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/libnvdimm-nd_blk-mask-off-reserved-status-bits.patch queue-4.7/mm-silently-skip-readahead-for-dax-inodes.patch