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mm: silently skip readahead for DAX inodes

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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/[email protected]
Signed-off-by: Ross Zwisler <[email protected]>
Reported-by: Jeff Moyer <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: <[email protected]>	[4.5+]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Ross Zwisler 2016-08-25 15:17:17 -07:00 • committed by Linus Torvalds
commit 11bd969fde
1 changed files with 9 additions and 0 deletions
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9
mm/readahead.c
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@ -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);
}