z3fold: limit use of stale list for allocation

Currently if z3fold couldn't find an unbuddied page it would first try
to pull a page off the stale list.  The problem with this approach is
that we can't 100% guarantee that the page is not processed by the
workqueue thread at the same time unless we run cancel_work_sync() on
it, which we can't do if we're in an atomic context.  So let's just
limit stale list usage to non-atomic contexts only.

Link: http://lkml.kernel.org/r/47ab51e7-e9c1-d30e-ab17-f734dbc3abce@gmail.com
Signed-off-by: Vitaly Vul <vitaly.vul@sony.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <Oleksiy.Avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/z3fold.c b/mm/z3fold.c
index d589d31..f579ad4 100644 (file)
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -620,24 +620,27 @@ lookup:
                bud = FIRST;
        }
 
-       spin_lock(&pool->stale_lock);
-       zhdr = list_first_entry_or_null(&pool->stale,
-                                       struct z3fold_header, buddy);
-       /*
-        * Before allocating a page, let's see if we can take one from the
-        * stale pages list. cancel_work_sync() can sleep so we must make
-        * sure it won't be called in case we're in atomic context.
-        */
-       if (zhdr && (can_sleep || !work_pending(&zhdr->work))) {
-               list_del(&zhdr->buddy);
-               spin_unlock(&pool->stale_lock);
-               if (can_sleep)
+       page = NULL;
+       if (can_sleep) {
+               spin_lock(&pool->stale_lock);
+               zhdr = list_first_entry_or_null(&pool->stale,
+                                               struct z3fold_header, buddy);
+               /*
+                * Before allocating a page, let's see if we can take one from
+                * the stale pages list. cancel_work_sync() can sleep so we
+                * limit this case to the contexts where we can sleep
+                */
+               if (zhdr) {
+                       list_del(&zhdr->buddy);
+                       spin_unlock(&pool->stale_lock);
                        cancel_work_sync(&zhdr->work);
-               page = virt_to_page(zhdr);
-       } else {
-               spin_unlock(&pool->stale_lock);
-               page = alloc_page(gfp);
+                       page = virt_to_page(zhdr);
+               } else {
+                       spin_unlock(&pool->stale_lock);
+               }
        }
+       if (!page)
+               page = alloc_page(gfp);
 
        if (!page)
                return -ENOMEM;