+ mm-silently-skip-readahead-for-dax-inodes.patch added to -mm tree

The patch titled
     Subject: mm: silently skip readahead for DAX inodes
has been added to the -mm tree.  Its filename is
     mm-silently-skip-readahead-for-dax-inodes.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-silently-skip-readahead-for-dax-inodes.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-silently-skip-readahead-for-dax-inodes.patch

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------------------------------------------------------
From: Ross Zwisler <redacted>
Subject: mm: silently skip readahead for DAX inodes

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.

Link: http://lkml.kernel.org/r/20160824221429.21158-1-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <redacted>
Reported-by: Jeff Moyer <redacted>
Cc: Dan Williams <redacted>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: <redacted>	[4.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

diff -puN mm/readahead.c~mm-silently-skip-readahead-for-dax-inodes mm/readahead.c

--- a/mm/readahead.c~mm-silently-skip-readahead-for-dax-inodes
+++ a/mm/readahead.c

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

@@ -544,6 +545,14 @@ 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 -mm which might be from ross.zwisler@linux.intel.com are

mm-silently-skip-readahead-for-dax-inodes.patch
radix-tree-slot-can-be-null-in-radix_tree_next_slot.patch
radix-tree-tests-add-iteration-test.patch
radix-tree-tests-properly-initialize-mutex.patch