From 01208951214460946b3c71d442663c65a8f5a96f Mon Sep 17 00:00:00 2001 From: Martin KaFai Lau Date: Thu, 17 Sep 2026 13:05:27 -0700 Subject: [PATCH] bpf: Remove __rcu tagging in st_link->map st_link->map is always written under update_mutex. The paths that read st_link->map with rcu_read_lock() are not in the fast path, so they can simply take update_mutex instead. Remove the __rcu annotation and replace all RCU accessors with direct pointer reads under update_mutex. Use READ_ONCE() in bpf_struct_ops_map_link_poll() which reads the pointer without holding update_mutex. It is a simplification change. Signed-off-by: Martin KaFai Lau Signed-off-by: Amery Hung Signed-off-by: Alexei Starovoitov Reviewed-by: Emil Tsalapatis Reviewed-by: Eduard Zingerman Link: https://patch.msgid.link/20260917200542.3689605-2-ameryhung@gmail.com --- kernel/bpf/bpf_struct_ops.c | 29 ++++++++++++++--------------- 1 file changed, 14 insertions(+), 15 deletions(-) diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index d7c3030bc63b..3935bf35a423 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -57,7 +57,7 @@ struct bpf_struct_ops_map { struct bpf_struct_ops_link { struct bpf_link link; - struct bpf_map __rcu *map; + struct bpf_map *map; wait_queue_head_t wait_hup; }; @@ -1297,8 +1297,7 @@ static void bpf_struct_ops_map_link_dealloc(struct bpf_link *link) struct bpf_struct_ops_map *st_map; st_link = container_of(link, struct bpf_struct_ops_link, link); - st_map = (struct bpf_struct_ops_map *) - rcu_dereference_protected(st_link->map, true); + st_map = (struct bpf_struct_ops_map *)st_link->map; if (st_map) { st_map->st_ops_desc->st_ops->unreg(&st_map->kvalue.data, link); bpf_map_put(&st_map->map); @@ -1313,11 +1312,11 @@ static void bpf_struct_ops_map_link_show_fdinfo(const struct bpf_link *link, struct bpf_map *map; st_link = container_of(link, struct bpf_struct_ops_link, link); - rcu_read_lock(); - map = rcu_dereference(st_link->map); + mutex_lock(&update_mutex); + map = st_link->map; if (map) seq_printf(seq, "map_id:\t%d\n", map->id); - rcu_read_unlock(); + mutex_unlock(&update_mutex); } static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, @@ -1327,11 +1326,11 @@ static int bpf_struct_ops_map_link_fill_link_info(const struct bpf_link *link, struct bpf_map *map; st_link = container_of(link, struct bpf_struct_ops_link, link); - rcu_read_lock(); - map = rcu_dereference(st_link->map); + mutex_lock(&update_mutex); + map = st_link->map; if (map) info->struct_ops.map_id = map->id; - rcu_read_unlock(); + mutex_unlock(&update_mutex); return 0; } @@ -1354,7 +1353,7 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map mutex_lock(&update_mutex); - old_map = rcu_dereference_protected(st_link->map, lockdep_is_held(&update_mutex)); + old_map = st_link->map; if (!old_map) { err = -ENOLINK; goto err_out; @@ -1376,7 +1375,7 @@ static int bpf_struct_ops_map_link_update(struct bpf_link *link, struct bpf_map goto err_out; bpf_map_inc(new_map); - rcu_assign_pointer(st_link->map, new_map); + WRITE_ONCE(st_link->map, new_map); bpf_map_put(old_map); err_out: @@ -1393,7 +1392,7 @@ static int bpf_struct_ops_map_link_detach(struct bpf_link *link) mutex_lock(&update_mutex); - map = rcu_dereference_protected(st_link->map, lockdep_is_held(&update_mutex)); + map = st_link->map; if (!map) { mutex_unlock(&update_mutex); return 0; @@ -1402,7 +1401,7 @@ static int bpf_struct_ops_map_link_detach(struct bpf_link *link) st_map->st_ops_desc->st_ops->unreg(&st_map->kvalue.data, link); - RCU_INIT_POINTER(st_link->map, NULL); + WRITE_ONCE(st_link->map, NULL); /* Pair with bpf_map_get() in bpf_struct_ops_link_create() or * bpf_map_inc() in bpf_struct_ops_map_link_update(). */ @@ -1422,7 +1421,7 @@ static __poll_t bpf_struct_ops_map_link_poll(struct file *file, poll_wait(file, &st_link->wait_hup, pts); - return rcu_access_pointer(st_link->map) ? 0 : EPOLLHUP; + return READ_ONCE(st_link->map) ? 0 : EPOLLHUP; } static const struct bpf_link_ops bpf_struct_ops_map_lops = { @@ -1478,7 +1477,7 @@ int bpf_struct_ops_link_create(union bpf_attr *attr) link = NULL; goto err_out; } - RCU_INIT_POINTER(link->map, map); + link->map = map; mutex_unlock(&update_mutex); return bpf_link_settle(&link_primer);