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filesystem-dax: Fix dax_layout_busy_page() livelock 

In the presence of multi-order entries the typical
pagevec_lookup_entries() pattern may loop forever:

	while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
				min(end - index, (pgoff_t)PAGEVEC_SIZE),
				indices)) {
		...
		for (i = 0; i < pagevec_count(&pvec); i++) {
			index = indices[i];
			...
		}
		index++; /* BUG */
	}

The loop updates 'index' for each index found and then increments to the
next possible page to continue the lookup. However, if the last entry in
the pagevec is multi-order then the next possible page index is more
than 1 page away. Fix this locally for the filesystem-dax case by
checking for dax-multi-order entries. Going forward new users of
multi-order entries need to be similarly careful, or we need a generic
way to report the page increment in the radix iterator.

Fixes: 5fac7408d8 ("mm, fs, dax: handle layout changes to pinned dax...")
Cc: <stable@vger.kernel.org>
Cc: Ross Zwisler <zwisler@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2018-10-06 10:56:11 -07:00
parent 17b57b1883
commit d7782145e1
1 changed files with 11 additions and 2 deletions
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13
fs/dax.c
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@ -666,6 +666,8 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE),
indices)) {
pgoff_t nr_pages = 1;
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *pvec_ent = pvec.pages[i];
void *entry;
@ -680,8 +682,15 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
xa_lock_irq(&mapping->i_pages);
entry = get_unlocked_mapping_entry(mapping, index, NULL);
if (entry)
if (entry) {
page = dax_busy_page(entry);
/*
* Account for multi-order entries at
* the end of the pagevec.
*/
if (i + 1 >= pagevec_count(&pvec))
nr_pages = 1UL << dax_radix_order(entry);
}
put_unlocked_mapping_entry(mapping, index, entry);
xa_unlock_irq(&mapping->i_pages);
if (page)
@ -696,7 +705,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
*/
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
index++;
index += nr_pages;
if (page)
break;