netdev - [PATCH 10/14] bpf: Re-initialize lnode in bpf_ksym

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Message-Id: <20200208154209.1797988-11-jolsa@kernel.org>
Date:   Sat,  8 Feb 2020 16:42:05 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>,
        Song Liu <songliubraving@...com>,
        Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...hat.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>
Subject: [PATCH 10/14] bpf: Re-initialize lnode in bpf_ksym_del

When bpf_prog is removed from kallsyms it's on the way
out to be removed, so we don't care about lnode state.

However the bpf_ksym_del will be used also by bpf_trampoline
and bpf_dispatcher objects, which stay allocated even when
they are not in kallsyms list, hence the lnode re-init.

The list_del_rcu commentary states that we need to call
synchronize_rcu, before we can change/re-init the list_head
pointers.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 kernel/bpf/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 73242fd07893..66b17bea286e 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -676,6 +676,13 @@ void bpf_ksym_del(struct bpf_ksym *ksym)
 	spin_lock_bh(&bpf_lock);
 	__bpf_ksym_del(ksym);
 	spin_unlock_bh(&bpf_lock);
+
+	/*
+	 * As explained in list_del_rcu, We must call synchronize_rcu
+	 * before changing list_head pointers.
+	 */
+	synchronize_rcu();
+	INIT_LIST_HEAD_RCU(&ksym->lnode);
 }
 
 static bool bpf_prog_kallsyms_candidate(const struct bpf_prog *fp)
-- 
2.24.1