Merge android-4.4-p.204 (583bdda) into msm-4.4

[sagit-ice-cold/kernel_xiaomi_msm8998.git] / mm / page-writeback.c

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 4087e77..d4492df 100644 (file)
--- 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;