[PATCH 5.0 025/238] dax: Flush partial PMDs correctly

From: Greg Kroah-Hartman
Date: Fri Mar 22 2019 - 08:33:43 EST

5.0-stable review patch. If anyone has any objections, please let me know.


From: Matthew Wilcox <willy@xxxxxxxxxxxxx>

commit e4b3448bc346fedf36db64124a664a959995b085 upstream.

The radix tree would rewind the index in an iterator to the lowest index
of a multi-slot entry. The XArray iterators instead leave the index
unchanged, but I overlooked that when converting DAX from the radix tree
to the XArray. Adjust the index that we use for flushing to the start
of the PMD range.

Fixes: c1901cd33cf4 ("page cache: Convert find_get_entries_tag to XArray")
Cc: <stable@xxxxxxxxxxxxxxx>
Reported-by: Piotr Balcer <piotr.balcer@xxxxxxxxx>
Tested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

fs/dax.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

--- a/fs/dax.c
+++ b/fs/dax.c
@@ -843,9 +843,8 @@ unlock_pte:
static int dax_writeback_one(struct xa_state *xas, struct dax_device *dax_dev,
struct address_space *mapping, void *entry)
- unsigned long pfn;
+ unsigned long pfn, index, count;
long ret = 0;
- size_t size;

* A page got tagged dirty in DAX mapping? Something is seriously
@@ -894,17 +893,18 @@ static int dax_writeback_one(struct xa_s

- * Even if dax_writeback_mapping_range() was given a wbc->range_start
- * in the middle of a PMD, the 'index' we are given will be aligned to
- * the start index of the PMD, as will the pfn we pull from 'entry'.
+ * If dax_writeback_mapping_range() was given a wbc->range_start
+ * in the middle of a PMD, the 'index' we use needs to be
+ * aligned to the start of the PMD.
* This allows us to flush for PMD_SIZE and not have to worry about
* partial PMD writebacks.
pfn = dax_to_pfn(entry);
- size = PAGE_SIZE << dax_entry_order(entry);
+ count = 1UL << dax_entry_order(entry);
+ index = xas->xa_index & ~(count - 1);

- dax_entry_mkclean(mapping, xas->xa_index, pfn);
- dax_flush(dax_dev, page_address(pfn_to_page(pfn)), size);
+ dax_entry_mkclean(mapping, index, pfn);
+ dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
* After we have flushed the cache, we can clear the dirty tag. There
* cannot be new dirty data in the pfn after the flush has completed as
@@ -917,8 +917,7 @@ static int dax_writeback_one(struct xa_s
xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
dax_wake_entry(xas, entry, false);

- trace_dax_writeback_one(mapping->host, xas->xa_index,
- size >> PAGE_SHIFT);
+ trace_dax_writeback_one(mapping->host, index, count);
return ret;