[bpf,v2,2/2] bpf: Use __llist_del_all() whenever possbile during memory draining

Commit Message

Hou Tao Oct. 21, 2022, 11:49 a.m. UTC

From: Hou Tao <[e-mail]>

Except for waiting_for_gp list, there are no concurrent operations on
free_by_rcu, free_llist and free_llist_extra lists, so use
__llist_del_all() instead of llist_del_all(). waiting_for_gp list can be
deleted by RCU callback concurrently, so still use llist_del_all().

Acked-by: Stanislav Fomichev <[e-mail]>
Signed-off-by: Hou Tao <[e-mail]>
---
 kernel/bpf/memalloc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Patch

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 4e4b3250aada..8f0d65f2474a 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -423,14 +423,17 @@  static void drain_mem_cache(struct bpf_mem_cache *c)
 	/* No progs are using this bpf_mem_cache, but htab_map_free() called
 	 * bpf_mem_cache_free() for all remaining elements and they can be in
 	 * free_by_rcu or in waiting_for_gp lists, so drain those lists now.
+	 *
+	 * Except for waiting_for_gp list, there are no concurrent operations
+	 * on these lists, so it is safe to use __llist_del_all().
 	 */
 	llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
 		free_one(c, llnode);
 	llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
 		free_one(c, llnode);
-	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
+	llist_for_each_safe(llnode, t, __llist_del_all(&c->free_llist))
 		free_one(c, llnode);
-	llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
+	llist_for_each_safe(llnode, t, __llist_del_all(&c->free_llist_extra))
 		free_one(c, llnode);
 }