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. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Reported-by: Jeff Moyer <jmoyer(a)redhat.com&gt; --- Changes from v1: - Added a comment so readers don't have to go putzing around in the git tree to understand why we're doing what we're doing. :) (akpm) --- mm/readahead.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/readahead.c b/mm/readahead.c index 65ec288..c8a955b 100644 --- a/mm/readahead.c +++ b/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 *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); } -- 2.9.0

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. Signed-off-by: Ross Zwisler <ross.zwisler(a)linux.intel.com&gt; Reported-by: Jeff Moyer <jmoyer(a)redhat.com&gt; Cc: <stable(a)vger.kernel.org&gt; [4.5+] --- Changes from v1: - Added a comment so readers don't have to go putzing around in the git tree to understand why we're doing what we're doing. :) (akpm) - Resending, adding stable(a)vger.kernel.org. Thank you, akpm, for the catch. --- mm/readahead.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/readahead.c b/mm/readahead.c index 65ec288..c8a955b 100644 --- a/mm/readahead.c +++ b/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 *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); } -- 2.9.0