netdev - [RFC PATCH] bpf: Fix potential call bpf_link

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Date:   Thu, 17 Sep 2020 15:44:53 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, andriin@...com,
        john.fastabend@...il.com, kpsingh@...omium.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: [RFC PATCH] bpf: Fix potential call bpf_link_free() in atomic context

The in_atomic macro cannot always detect atomic context. In particular,
it cannot know about held spinlocks in non-preemptible kernels. Although,
there is no user call bpf_link_put() with holding spinlock now. Be the
safe side, we can avoid this in the feature.

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 kernel/bpf/syscall.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 178c147350f5..6347be0a5c82 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2345,12 +2345,8 @@ void bpf_link_put(struct bpf_link *link)
 	if (!atomic64_dec_and_test(&link->refcnt))
 		return;
 
-	if (in_atomic()) {
-		INIT_WORK(&link->work, bpf_link_put_deferred);
-		schedule_work(&link->work);
-	} else {
-		bpf_link_free(link);
-	}
+	INIT_WORK(&link->work, bpf_link_put_deferred);
+	schedule_work(&link->work);
 }
 
 static int bpf_link_release(struct inode *inode, struct file *filp)
-- 
2.20.1