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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/slub.c b/mm/slub.c
index 8f78e25..2fdd96f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1524,12 +1524,13 @@
}
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;
@@ -1545,9 +1546,13 @@
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;
@@ -1614,7 +1619,7 @@
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
@@ -1643,7 +1648,7 @@
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;