bpf: Add a few bpf mem allocator functions

This patch adds a few bpf mem allocator functions which will
be used in the bpf_local_storage in a later patch.

bpf_mem_cache_alloc_flags(..., gfp_t flags) is added. When the
flags == GFP_KERNEL, it will fallback to __alloc(..., GFP_KERNEL).
bpf_local_storage knows its running context is sleepable (GFP_KERNEL)
and provides a better guarantee on memory allocation.

bpf_local_storage has some uncommon cases that its selem
cannot be reused immediately. It handles its own
rcu_head and goes through a rcu_trace gp and then free it.
bpf_mem_cache_raw_free() is added for direct free purpose
without leaking the LLIST_NODE_SZ internal knowledge.
During free time, the 'struct bpf_mem_alloc *ma' is no longer
available. However, the caller should know if it is
percpu memory or not and it can call different raw_free functions.
bpf_local_storage does not support percpu value, so only
the non-percpu 'bpf_mem_cache_raw_free()' is added in
this patch.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/r/20230322215246.1675516-2-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf_mem_alloc.h b/include/linux/bpf_mem_alloc.h
index a7104af..3929be5 100644 (file)
--- a/include/linux/bpf_mem_alloc.h
+++ b/include/linux/bpf_mem_alloc.h
@@ -31,5 +31,7 @@ void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr);
 /* kmem_cache_alloc/free equivalent: */
 void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma);
 void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr);
+void bpf_mem_cache_raw_free(void *ptr);
+void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags);
 
 #endif /* _BPF_MEM_ALLOC_H */

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 5fcdacb..410637c 100644 (file)
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -121,15 +121,8 @@ static struct llist_node notrace *__llist_del_first(struct llist_head *head)
        return entry;
 }
 
-static void *__alloc(struct bpf_mem_cache *c, int node)
+static void *__alloc(struct bpf_mem_cache *c, int node, gfp_t flags)
 {
-       /* Allocate, but don't deplete atomic reserves that typical
-        * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
-        * will allocate from the current numa node which is what we
-        * want here.
-        */
-       gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
-
        if (c->percpu_size) {
                void **obj = kmalloc_node(c->percpu_size, flags, node);
                void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
@@ -185,7 +178,12 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
                 */
                obj = __llist_del_first(&c->free_by_rcu);
                if (!obj) {
-                       obj = __alloc(c, node);
+                       /* Allocate, but don't deplete atomic reserves that typical
+                        * GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
+                        * will allocate from the current numa node which is what we
+                        * want here.
+                        */
+                       obj = __alloc(c, node, GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT);
                        if (!obj)
                                break;
                }
@@ -676,3 +674,46 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
 
        unit_free(this_cpu_ptr(ma->cache), ptr);
 }
+
+/* Directly does a kfree() without putting 'ptr' back to the free_llist
+ * for reuse and without waiting for a rcu_tasks_trace gp.
+ * The caller must first go through the rcu_tasks_trace gp for 'ptr'
+ * before calling bpf_mem_cache_raw_free().
+ * It could be used when the rcu_tasks_trace callback does not have
+ * a hold on the original bpf_mem_alloc object that allocated the
+ * 'ptr'. This should only be used in the uncommon code path.
+ * Otherwise, the bpf_mem_alloc's free_llist cannot be refilled
+ * and may affect performance.
+ */
+void bpf_mem_cache_raw_free(void *ptr)
+{
+       if (!ptr)
+               return;
+
+       kfree(ptr - LLIST_NODE_SZ);
+}
+
+/* When flags == GFP_KERNEL, it signals that the caller will not cause
+ * deadlock when using kmalloc. bpf_mem_cache_alloc_flags() will use
+ * kmalloc if the free_llist is empty.
+ */
+void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags)
+{
+       struct bpf_mem_cache *c;
+       void *ret;
+
+       c = this_cpu_ptr(ma->cache);
+
+       ret = unit_alloc(c);
+       if (!ret && flags == GFP_KERNEL) {
+               struct mem_cgroup *memcg, *old_memcg;
+
+               memcg = get_memcg(c);
+               old_memcg = set_active_memcg(memcg);
+               ret = __alloc(c, NUMA_NO_NODE, GFP_KERNEL | __GFP_NOWARN | __GFP_ACCOUNT);
+               set_active_memcg(old_memcg);
+               mem_cgroup_put(memcg);
+       }
+
+       return !ret ? NULL : ret + LLIST_NODE_SZ;
+}