linux-kernel - [PATCH] bpf: force inc_active()/dec

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Date:   Sat, 22 Jul 2023 09:47:44 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Hou Tao <houtao1@...wei.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] bpf: force inc_active()/dec_active() to be inline functions

From: Arnd Bergmann <arnd@...db.de>

Splitting these out into separate helper functions means that we
actually pass an uninitialized variable into another function call
if dec_active() happens to not be inlined, and CONFIG_PREEMPT_RT
is disabled:

kernel/bpf/memalloc.c: In function 'add_obj_to_free_list':
kernel/bpf/memalloc.c:200:9: error: 'flags' is used uninitialized [-Werror=uninitialized]
  200 |         dec_active(c, flags);

Mark the two functions as __always_inline so gcc can see through
this regardless of optimizations and other options that may
prevent it otherwise.

Fixes: 18e027b1c7c6d ("bpf: Factor out inc/dec of active flag into helpers.")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 kernel/bpf/memalloc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 51d6389e5152e..23906325298da 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -165,7 +165,7 @@ static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
 #endif
 }
 
-static void inc_active(struct bpf_mem_cache *c, unsigned long *flags)
+static __always_inline void inc_active(struct bpf_mem_cache *c, unsigned long *flags)
 {
 	if (IS_ENABLED(CONFIG_PREEMPT_RT))
 		/* In RT irq_work runs in per-cpu kthread, so disable
@@ -183,7 +183,7 @@ static void inc_active(struct bpf_mem_cache *c, unsigned long *flags)
 	WARN_ON_ONCE(local_inc_return(&c->active) != 1);
 }
 
-static void dec_active(struct bpf_mem_cache *c, unsigned long flags)
+static __always_inline void dec_active(struct bpf_mem_cache *c, unsigned long flags)
 {
 	local_dec(&c->active);
 	if (IS_ENABLED(CONFIG_PREEMPT_RT))
-- 
2.39.2