X-Git-Url: http://git.osdn.net/view?a=blobdiff_plain;f=mm%2Fpage-writeback.c;h=d4492df0ea81fa77f40cbf6eaa38ea1670246f0a;hb=ed0754412226e593ffccb7990b18eb4914ac77e7;hp=4087e77cd0338ab89d87f9e5f61297eaa375f926;hpb=defeb52f60ad863f571dc25e645b551e25b5b94f;p=sagit-ice-cold%2Fkernel_xiaomi_msm8998.git

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4087e77cd033..d4492df0ea81 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2160,6 +2160,13 @@ EXPORT_SYMBOL(tag_pages_for_writeback);
  * not miss some pages (e.g., because some other process has cleared TOWRITE
  * tag we set). The rule we follow is that TOWRITE tag can be cleared only
  * by the process clearing the DIRTY tag (and submitting the page for IO).
+ *
+ * To avoid deadlocks between range_cyclic writeback and callers that hold
+ * pages in PageWriteback to aggregate IO until write_cache_pages() returns,
+ * we do not loop back to the start of the file. Doing so causes a page
+ * lock/page writeback access order inversion - we should only ever lock
+ * multiple pages in ascending page->index order, and looping back to the start
+ * of the file violates that rule and causes deadlocks.
  */
 int write_cache_pages(struct address_space *mapping,
 		      struct writeback_control *wbc, writepage_t writepage,
@@ -2174,7 +2181,6 @@ int write_cache_pages(struct address_space *mapping,
 	pgoff_t index;
 	pgoff_t end;		/* Inclusive */
 	pgoff_t done_index;
-	int cycled;
 	int range_whole = 0;
 	int tag;
 
@@ -2182,23 +2188,17 @@ int write_cache_pages(struct address_space *mapping,
 	if (wbc->range_cyclic) {
 		writeback_index = mapping->writeback_index; /* prev offset */
 		index = writeback_index;
-		if (index == 0)
-			cycled = 1;
-		else
-			cycled = 0;
 		end = -1;
 	} else {
 		index = wbc->range_start >> PAGE_CACHE_SHIFT;
 		end = wbc->range_end >> PAGE_CACHE_SHIFT;
 		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
 			range_whole = 1;
-		cycled = 1; /* ignore range_cyclic tests */
 	}
 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
 		tag = PAGECACHE_TAG_TOWRITE;
 	else
 		tag = PAGECACHE_TAG_DIRTY;
-retry:
 	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
 		tag_pages_for_writeback(mapping, index, end);
 	done_index = index;
@@ -2290,17 +2290,14 @@ continue_unlock:
 		pagevec_release(&pvec);
 		cond_resched();
 	}
-	if (!cycled && !done) {
-		/*
-		 * range_cyclic:
-		 * We hit the last page and there is more work to be done: wrap
-		 * back to the start of the file
-		 */
-		cycled = 1;
-		index = 0;
-		end = writeback_index - 1;
-		goto retry;
-	}
+
+	/*
+	 * If we hit the last page and there is more work to be done: wrap
+	 * back the index back to the start of the file for the next
+	 * time we are called.
+	 */
+	if (wbc->range_cyclic && !done)
+		done_index = 0;
 	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
 		mapping->writeback_index = done_index;