[PATCH] Remove semi-softlockup from invalidate_mapping_pages

If invalidate_mapping_pages is called to invalidate a very large mapping
(e.g.  a very large block device) and if the only active page in that
device is near the end (or at least, at a very large index), such as, say,
the superblock of an md array, and if that page happens to be locked when
invalidate_mapping_pages is called, then

  pagevec_lookup will return this page and
  as it is locked, 'next' will be incremented and pagevec_lookup
  will be called again. and again. and again.
  while we count from 0 upto a very large number.

We should really always set 'next' to 'page->index+1' before going around
the loop again, not just if the page isn't locked.

Cc: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 16 insertions, 6 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 6cb3fff25f67..cf1b015df4a7 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -230,14 +230,24 @@ unsigned long invalidate_mapping_pages(struct address_space *mapping,
                         pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
                 for (i = 0; i < pagevec_count(&pvec); i++) {
                         struct page *page = pvec.pages[i];
+                        pgoff_t index;
+                        int lock_failed;
 
-                        if (TestSetPageLocked(page)) {
-                                next++;
-                                continue;
-                        }
-                        if (page->index > next)
-                                next = page->index;
+                        lock_failed = TestSetPageLocked(page);
+
+                        /*
+                         * We really shouldn't be looking at the ->index of an
+                         * unlocked page.  But we're not allowed to lock these
+                         * pages.  So we rely upon nobody altering the ->index
+                         * of this (pinned-by-us) page.
+                         */
+                        index = page->index;
+                        if (index > next)
+                                next = index;
                         next++;
+                        if (lock_failed)
+                                continue;
+
                         if (PageDirty(page) || PageWriteback(page))
                                 goto unlock;
                         if (page_mapped(page))