Commit 11bd969f authored Aug 25, 2016 by Ross Zwisler Committed by Linus Torvalds Aug 26, 2016

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 <ross.zwisler@linux.intel.com>
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: <stable@vger.kernel.org>	[4.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d0e58455

mm/readahead.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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 mapping, struct file filp,
		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);
		}

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