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From:   Stijn Tintel <stijn@linux-ipv6.be>
To:     toke@redhat.com, netdev@vger.kernel.org
Cc:     bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        kpsingh@kernel.org, john.fastabend@gmail.com, yhs@fb.com,
        songliubraving@fb.com, kafai@fb.com, andrii@kernel.org,
        daniel@iogearbox.net, ast@kernel.org
Subject: [PATCH] libbpf: fix BPF_MAP_TYPE_PERF_EVENT_ARRAY auto-pinning
Date:   Tue, 22 Feb 2022 22:42:36 +0200
Message-Id: <20220222204236.2192513-1-stijn@linux-ipv6.be>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

When a BPF map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY doesn't have the
max_entries parameter set, this parameter will be set to the number of
possible CPUs. Due to this, the map_is_reuse_compat function will return
false, causing the following error when trying to reuse the map:

libbpf: couldn't reuse pinned map at '/sys/fs/bpf/m_logging': parameter m=
ismatch

Fix this by checking against the number of possible CPUs if the
max_entries parameter is not set in the map definition.

Fixes: 57a00f41644f ("libbpf: Add auto-pinning of maps when loading BPF o=
bjects")
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
---
 tools/lib/bpf/libbpf.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7f10dd501a52..b076ab728f0e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4750,7 +4750,7 @@ static bool map_is_reuse_compat(const struct bpf_ma=
p *map, int map_fd)
 	struct bpf_map_info map_info =3D {};
 	char msg[STRERR_BUFSIZE];
 	__u32 map_info_len;
-	int err;
+	int def_max_entries, err;
=20
 	map_info_len =3D sizeof(map_info);
=20
@@ -4763,10 +4763,15 @@ static bool map_is_reuse_compat(const struct bpf_=
map *map, int map_fd)
 		return false;
 	}
=20
+	if (map->def.type =3D=3D BPF_MAP_TYPE_PERF_EVENT_ARRAY && !map->def.max=
_entries)
+		def_max_entries =3D libbpf_num_possible_cpus();
+	else
+		def_max_entries =3D map->def.max_entries;
+
 	return (map_info.type =3D=3D map->def.type &&
 		map_info.key_size =3D=3D map->def.key_size &&
 		map_info.value_size =3D=3D map->def.value_size &&
-		map_info.max_entries =3D=3D map->def.max_entries &&
+		map_info.max_entries =3D=3D def_max_entries &&
 		map_info.map_flags =3D=3D map->def.map_flags &&
 		map_info.map_extra =3D=3D map->map_extra);
 }
--=20
2.34.1