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authorHugh Dickins <hughd@google.com>2011-03-22 16:33:06 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:04 -0700
commit9d8aa4ea855e0d64bb6926acb5618e6d1e2ed344 (patch)
treea21357f21084169e0a322f8fa8ce8abe343d4f06
parentc033a93c0d961fc7ec5b0872649143e061d97dd4 (diff)
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 <hughd@google.com> Cc: Nick Piggin <npiggin@kernel.dk> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Salman Qazi <sqazi@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/filemap.c18
1 files changed, 16 insertions, 2 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index cb476e70cf19..a29318147365 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;