From 9d8aa4ea855e0d64bb6926acb5618e6d1e2ed344 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 22 Mar 2011 16:33:06 -0700 Subject: mm: remove worrying dead code from find_get_pages() The radix_tree_deref_retry() case in find_get_pages() has a strange little excrescence, not seen in the other gang lookups: it looks like the start of an abandoned attempt to guarantee forward progress in a case that cannot arise. ret should always be 0 here: if it isn't, then going back to restart will leak references to pages already gotten. There used to be a comment saying nr_found is necessarily 1 here: that's not quite true, but the radix_tree_deref_retry() case is peculiar to the entry at index 0, when we race with it being moved out of the radix_tree root or back. Remove the worrisome two lines, add a brief comment here and in find_get_pages_contig() and find_get_pages_tag(), and a WARN_ON in find_get_pages() should it ever be seen elsewhere than at 0. Signed-off-by: Hugh Dickins Cc: Nick Piggin Acked-by: Peter Zijlstra Cc: Wu Fengguang Cc: Salman Qazi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index cb476e70cf1..a2931814736 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -863,9 +863,13 @@ repeat: page = radix_tree_deref_slot((void **)pages[i]); if (unlikely(!page)) continue; + + /* + * This can only trigger when the entry at index 0 moves out + * of or back to the root: none yet gotten, safe to restart. + */ if (radix_tree_deref_retry(page)) { - if (ret) - start = pages[ret-1]->index; + WARN_ON(start | i); goto restart; } @@ -915,6 +919,11 @@ repeat: page = radix_tree_deref_slot((void **)pages[i]); if (unlikely(!page)) continue; + + /* + * This can only trigger when the entry at index 0 moves out + * of or back to the root: none yet gotten, safe to restart. + */ if (radix_tree_deref_retry(page)) goto restart; @@ -975,6 +984,11 @@ repeat: page = radix_tree_deref_slot((void **)pages[i]); if (unlikely(!page)) continue; + + /* + * This can only trigger when the entry at index 0 moves out + * of or back to the root: none yet gotten, safe to restart. + */ if (radix_tree_deref_retry(page)) goto restart; -- cgit v1.2.3