[PATCH] valid_swaphandles() fix

akpm draws my attention to the fact that sysctl(VM_PAGE_CLUSTER) might
conceivably change page_cluster to 0 while valid_swaphandles() is in the
middle of using it, leading to an embarrassingly long loop: take a local
snapshot of page_cluster and work with that.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index f1f5ec783781..a15def63f28f 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1723,13 +1723,14 @@ get_swap_info_struct(unsigned type)
  */
 int valid_swaphandles(swp_entry_t entry, unsigned long *offset)
 {
-        int ret = 0, i = 1 << page_cluster;
+        int our_page_cluster = page_cluster;
+        int ret = 0, i = 1 << our_page_cluster;
         unsigned long toff;
         struct swap_info_struct *swapdev = swp_type(entry) + swap_info;
 
-        if (!page_cluster)      /* no readahead */
+        if (!our_page_cluster)  /* no readahead */
                 return 0;
-        toff = (swp_offset(entry) >> page_cluster) << page_cluster;
+        toff = (swp_offset(entry) >> our_page_cluster) << our_page_cluster;
         if (!toff)              /* first page is swap header */
                 toff++, i--;
         *offset = toff;