Subject: [PATCH 10/18] bpf: Re-initialize lnode in bpf_ksym_del

From: Jiri Olsa <[email-masked]>
Date: Sun, 16 Feb 2020 20:29:57 +0100

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 <[email-masked]>
---
 kernel/bpf/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 739bef60d868..a0feba447e5d 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