Commit 8ba00bb6 authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Linus Torvalds

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: default avatarJoonsoo Kim <>
Acked-by: default avatarDavid Rientjes <>
Signed-off-by: default avatarMel Gorman <>
Cc: David Miller <>
Cc: Chuck Lever <>
Cc: Pekka Enberg <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent d014dc2e
......@@ -1524,12 +1524,13 @@ 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;
......@@ -1545,9 +1546,13 @@ static void *get_partial_node(struct kmem_cache *s,
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))
t = acquire_slab(s, n, page, object == NULL);
if (!t)
......@@ -1614,7 +1619,7 @@ 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
......@@ -1643,7 +1648,7 @@ 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;
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