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" Reported-by: Piotr Balcer <piotr.balcer(a)intel.com&gt; Tested-by: Dan Williams <dan.j.williams(a)intel.com&gt; Signed-off-by: Matthew Wilcox <willy(a)infradead.org&gt; --- fs/dax.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 6959837cc465..4116cd9f55dd 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -843,9 +843,8 @@ static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index, 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, xas->xa_index, count); return ret; put_unlocked: -- 2.20.1