page_pool: fix logic in __page_pool_get_cached

__page_pool_get_cached() will return NULL when the ring is
empty, even if there are pages present in the lookaside cache.

It is also possible to refill the cache, and then return a
NULL page.

Restructure the logic so eliminate both cases.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 31187ff..5bc6558 100644 (file)
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -82,12 +82,9 @@ EXPORT_SYMBOL(page_pool_create);
 static struct page *__page_pool_get_cached(struct page_pool *pool)
 {
        struct ptr_ring *r = &pool->ring;
+       bool refill = false;
        struct page *page;
 
-       /* Quicker fallback, avoid locks when ring is empty */
-       if (__ptr_ring_empty(r))
-               return NULL;
-
        /* Test for safe-context, caller should provide this guarantee */
        if (likely(in_serving_softirq())) {
                if (likely(pool->alloc.count)) {
@@ -95,27 +92,23 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
                        page = pool->alloc.cache[--pool->alloc.count];
                        return page;
                }
-               /* Slower-path: Alloc array empty, time to refill
-                *
-                * Open-coded bulk ptr_ring consumer.
-                *
-                * Discussion: the ring consumer lock is not really
-                * needed due to the softirq/NAPI protection, but
-                * later need the ability to reclaim pages on the
-                * ring. Thus, keeping the locks.
-                */
-               spin_lock(&r->consumer_lock);
-               while ((page = __ptr_ring_consume(r))) {
-                       if (pool->alloc.count == PP_ALLOC_CACHE_REFILL)
-                               break;
-                       pool->alloc.cache[pool->alloc.count++] = page;
-               }
-               spin_unlock(&r->consumer_lock);
-               return page;
+               refill = true;
        }
 
-       /* Slow-path: Get page from locked ring queue */
-       page = ptr_ring_consume(&pool->ring);
+       /* Quicker fallback, avoid locks when ring is empty */
+       if (__ptr_ring_empty(r))
+               return NULL;
+
+       /* Slow-path: Get page from locked ring queue,
+        * refill alloc array if requested.
+        */
+       spin_lock(&r->consumer_lock);
+       page = __ptr_ring_consume(r);
+       if (refill)
+               pool->alloc.count = __ptr_ring_consume_batched(r,
+                                                       pool->alloc.cache,
+                                                       PP_ALLOC_CACHE_REFILL);
+       spin_unlock(&r->consumer_lock);
        return page;
 }