dax: Flush partial PMDs correctly

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@vger.kernel.org>
Reported-by: Piotr Balcer <piotr.balcer@intel.com>
Tested-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/dax.c b/fs/dax.c
index c55afa4..ca0671d 100644 (file)
--- 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_state *xas, struct dax_device *dax_dev,
        xas_unlock_irq(xas);
 
        /*
-        * 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_state *xas, struct dax_device *dax_dev,
        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;
 
  put_unlocked: