[PATCH bpf-next v3 1/2] bpf: Make non-preallocated allocation low priority

[Yafang Shao <laoar.shao@gmail.com>]

GFP_ATOMIC doesn't cooperate well with memcg pressure so far, especially
if we allocate too much GFP_ATOMIC memory. For example, when we set the
memcg limit to limit a non-preallocated bpf memory, the GFP_ATOMIC can
easily break the memcg limit by force charge. So it is very dangerous to
use GFP_ATOMIC in non-preallocated case. One way to make it safe is to
remove __GFP_HIGH from GFP_ATOMIC, IOW, use (__GFP_ATOMIC |
__GFP_KSWAPD_RECLAIM) instead, then it will be limited if we allocate
too much memory. There's a plan to completely remove __GFP_ATOMIC in the
mm side[1], so let's use GFP_NOWAIT instead.

We introduced BPF_F_NO_PREALLOC is because full map pre-allocation is
too memory expensive for some cases. That means removing __GFP_HIGH
doesn't break the rule of BPF_F_NO_PREALLOC, but has the same goal with
it-avoiding issues caused by too much memory. So let's remove it.

This fix can also apply to other run-time allocations, for example, the
allocation in lpm trie, local storage and devmap. So let fix it
consistently over the bpf code

It also fixes a typo in the comment.

[1]. https://lore.kernel.org/linux-mm/163712397076.13692.4727608274002939094@noble.neil.brown.name/

Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: NeilBrown <neilb@suse.de>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 kernel/bpf/devmap.c        | 2 +-
 kernel/bpf/hashtab.c       | 6 +++---
 kernel/bpf/local_storage.c | 2 +-
 kernel/bpf/lpm_trie.c      | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index c2867068e5bd..1400561efb15 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -845,7 +845,7 @@ static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
 	struct bpf_dtab_netdev *dev;
 
 	dev = bpf_map_kmalloc_node(&dtab->map, sizeof(*dev),
-				   GFP_ATOMIC | __GFP_NOWARN,
+				   GFP_NOWAIT | __GFP_NOWARN,
 				   dtab->map.numa_node);
 	if (!dev)
 		return ERR_PTR(-ENOMEM);
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 17fb69c0e0dc..da7578426a46 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -61,7 +61,7 @@
  *
  * As regular device interrupt handlers and soft interrupts are forced into
  * thread context, the existing code which does
- *   spin_lock*(); alloc(GPF_ATOMIC); spin_unlock*();
+ *   spin_lock*(); alloc(GFP_ATOMIC); spin_unlock*();
  * just works.
  *
  * In theory the BPF locks could be converted to regular spinlocks as well,
@@ -978,7 +978,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 				goto dec_count;
 			}
 		l_new = bpf_map_kmalloc_node(&htab->map, htab->elem_size,
-					     GFP_ATOMIC | __GFP_NOWARN,
+					     GFP_NOWAIT | __GFP_NOWARN,
 					     htab->map.numa_node);
 		if (!l_new) {
 			l_new = ERR_PTR(-ENOMEM);
@@ -996,7 +996,7 @@ static struct htab_elem *alloc_htab_elem(struct bpf_htab *htab, void *key,
 		} else {
 			/* alloc_percpu zero-fills */
 			pptr = bpf_map_alloc_percpu(&htab->map, size, 8,
-						    GFP_ATOMIC | __GFP_NOWARN);
+						    GFP_NOWAIT | __GFP_NOWARN);
 			if (!pptr) {
 				kfree(l_new);
 				l_new = ERR_PTR(-ENOMEM);
diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
index 8654fc97f5fe..49ef0ce040c7 100644
--- a/kernel/bpf/local_storage.c
+++ b/kernel/bpf/local_storage.c
@@ -165,7 +165,7 @@ static int cgroup_storage_update_elem(struct bpf_map *map, void *key,
 	}
 
 	new = bpf_map_kmalloc_node(map, struct_size(new, data, map->value_size),
-				   __GFP_ZERO | GFP_ATOMIC | __GFP_NOWARN,
+				   __GFP_ZERO | GFP_NOWAIT | __GFP_NOWARN,
 				   map->numa_node);
 	if (!new)
 		return -ENOMEM;
diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index f0d05a3cc4b9..d789e3b831ad 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -285,7 +285,7 @@ static struct lpm_trie_node *lpm_trie_node_alloc(const struct lpm_trie *trie,
 	if (value)
 		size += trie->map.value_size;
 
-	node = bpf_map_kmalloc_node(&trie->map, size, GFP_ATOMIC | __GFP_NOWARN,
+	node = bpf_map_kmalloc_node(&trie->map, size, GFP_NOWAIT | __GFP_NOWARN,
 				    trie->map.numa_node);
 	if (!node)
 		return NULL;
-- 
2.17.1