netdev - [PATCH bpf] bpf: sockmap: add locking annotations to iterator

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Date:   Mon, 12 Oct 2020 11:18:50 +0200
From:   Lorenz Bauer <lmb@...udflare.com>
To:     John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>, Yonghong Song <yhs@...com>
Cc:     kernel-team@...udflare.com, kernel test robot <lkp@...el.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH bpf] bpf: sockmap: add locking annotations to iterator

The sparse checker currently outputs the following warnings:

    include/linux/rcupdate.h:632:9: sparse: sparse: context imbalance in 'sock_hash_seq_start' - wrong count at exit
    include/linux/rcupdate.h:632:9: sparse: sparse: context imbalance in 'sock_map_seq_start' - wrong count at exit

Add the necessary __acquires and __release annotations to make the
iterator locking schema palatable to sparse. Also add __must_hold
for good measure.

The kernel codebase uses both __acquires(rcu) and __acquires(RCU).
I couldn't find any guidance which one is preferred, so I used
what is easier to type out.

Fixes: 0365351524d7 ("net: Allow iterating sockmap and sockhash")
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
---
 net/core/sock_map.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index df09c39a4dd2..203900a6ca5f 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -745,6 +745,7 @@ static void *sock_map_seq_lookup_elem(struct sock_map_seq_info *info)
 }
 
 static void *sock_map_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(rcu)
 {
 	struct sock_map_seq_info *info = seq->private;
 
@@ -757,6 +758,7 @@ static void *sock_map_seq_start(struct seq_file *seq, loff_t *pos)
 }
 
 static void *sock_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+	__must_hold(rcu)
 {
 	struct sock_map_seq_info *info = seq->private;
 
@@ -767,6 +769,7 @@ static void *sock_map_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static int sock_map_seq_show(struct seq_file *seq, void *v)
+	__must_hold(rcu)
 {
 	struct sock_map_seq_info *info = seq->private;
 	struct bpf_iter__sockmap ctx = {};
@@ -789,6 +792,7 @@ static int sock_map_seq_show(struct seq_file *seq, void *v)
 }
 
 static void sock_map_seq_stop(struct seq_file *seq, void *v)
+	__releases(rcu)
 {
 	if (!v)
 		(void)sock_map_seq_show(seq, NULL);
@@ -1353,6 +1357,7 @@ static void *sock_hash_seq_find_next(struct sock_hash_seq_info *info,
 }
 
 static void *sock_hash_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(rcu)
 {
 	struct sock_hash_seq_info *info = seq->private;
 
@@ -1365,6 +1370,7 @@ static void *sock_hash_seq_start(struct seq_file *seq, loff_t *pos)
 }
 
 static void *sock_hash_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+	__must_hold(rcu)
 {
 	struct sock_hash_seq_info *info = seq->private;
 
@@ -1373,6 +1379,7 @@ static void *sock_hash_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static int sock_hash_seq_show(struct seq_file *seq, void *v)
+	__must_hold(rcu)
 {
 	struct sock_hash_seq_info *info = seq->private;
 	struct bpf_iter__sockmap ctx = {};
@@ -1396,6 +1403,7 @@ static int sock_hash_seq_show(struct seq_file *seq, void *v)
 }
 
 static void sock_hash_seq_stop(struct seq_file *seq, void *v)
+	__releases(rcu)
 {
 	if (!v)
 		(void)sock_hash_seq_show(seq, NULL);
-- 
2.25.1