slub: consider pfmemalloc_match() in get_partial_node()

get_partial() is currently not checking pfmemalloc_match() meaning that it
is possible for pfmemalloc pages to leak to non-pfmemalloc users.  This is
a problem in the following situation.  Assume that there is a request from
normal allocation and there are no objects in the per-cpu cache and no
node-partial slab.

In this case, slab_alloc enters the slow path and new_slab_objects() is
called which may return a PFMEMALLOC page.  As the current user is not
allowed to access PFMEMALLOC page, deactivate_slab() is called ([5091b74a:
mm: slub: optimise the SLUB fast path to avoid pfmemalloc checks]) and
returns an object from PFMEMALLOC page.

Next time, when we get another request from normal allocation,
slab_alloc() enters the slow-path and calls new_slab_objects().  In
new_slab_objects(), we call get_partial() and get a partial slab which was
just deactivated but is a pfmemalloc page.  We extract one object from it
and re-deactivate.

"deactivate -> re-get in get_partial -> re-deactivate" occures repeatedly.

As a result, access to PFMEMALLOC page is not properly restricted and it
can cause a performance degradation due to frequent deactivation.
deactivation frequently.

This patch changes get_partial_node() to take pfmemalloc_match() into
account and prevents the "deactivate -> re-get in get_partial() scenario.
Instead, new_slab() is called.

Signed-off-by: Joonsoo Kim <js1304@gmail.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: David Miller <davem@davemloft.net>
Cc: Chuck Lever <chuck.lever@oracle.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/slub.c b/mm/slub.c
index 2258ed82880a063eee70893f26664e635d7d04a0..628a26101c07aa500eeac6696e0a475adcb0d112 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1525,12 +1525,13 @@ static inline void *acquire_slab(struct kmem_cache *s,
 }
 
 static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain);
+static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags);
 
 /*
  * Try to allocate a partial slab from a specific node.
  */
-static void *get_partial_node(struct kmem_cache *s,
-               struct kmem_cache_node *n, struct kmem_cache_cpu *c)
+static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
+                               struct kmem_cache_cpu *c, gfp_t flags)
 {
        struct page *page, *page2;
        void *object = NULL;
@@ -1546,9 +1547,13 @@ static void *get_partial_node(struct kmem_cache *s,
 
        spin_lock(&n->list_lock);
        list_for_each_entry_safe(page, page2, &n->partial, lru) {
-               void *t = acquire_slab(s, n, page, object == NULL);
+               void *t;
                int available;
 
+               if (!pfmemalloc_match(page, flags))
+                       continue;
+
+               t = acquire_slab(s, n, page, object == NULL);
                if (!t)
                        break;
 
@@ -1615,7 +1620,7 @@ static void *get_any_partial(struct kmem_cache *s, gfp_t flags,
 
                        if (n && cpuset_zone_allowed_hardwall(zone, flags) &&
                                        n->nr_partial > s->min_partial) {
-                               object = get_partial_node(s, n, c);
+                               object = get_partial_node(s, n, c, flags);
                                if (object) {
                                        /*
                                         * Return the object even if
@@ -1644,7 +1649,7 @@ static void *get_partial(struct kmem_cache *s, gfp_t flags, int node,
        void *object;
        int searchnode = (node == NUMA_NO_NODE) ? numa_node_id() : node;
 
-       object = get_partial_node(s, get_node(s, searchnode), c);
+       object = get_partial_node(s, get_node(s, searchnode), c, flags);
        if (object || node != NUMA_NO_NODE)
                return object;