netdev - [PATCH bpf] cpumap: Avoid warning when CONFIG_DEBUG_PER_CPU

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Message-Id: <20200415140151.439943-1-toke@redhat.com>
Date:   Wed, 15 Apr 2020 16:01:51 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     daniel@...earbox.net, ast@...com
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        bpf@...r.kernel.org, netdev@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Xiumei Mu <xmu@...hat.com>
Subject: [PATCH bpf] cpumap: Avoid warning when CONFIG_DEBUG_PER_CPU_MAPS is enabled

When the kernel is built with CONFIG_DEBUG_PER_CPU_MAPS, the cpumap code
can trigger a spurious warning if CONFIG_CPUMASK_OFFSTACK is also set. This
happens because in this configuration, NR_CPUS can be larger than
nr_cpumask_bits, so the initial check in cpu_map_alloc() is not sufficient
to guard against hitting the warning in cpumask_check().

Fix this by using the nr_cpumask_bits variable in the map creation code
instead of the NR_CPUS constant.

Fixes: 6710e1126934 ("bpf: introduce new bpf cpu map type BPF_MAP_TYPE_CPUMAP")
Cc: Jesper Dangaard Brouer <brouer@...hat.com>
Reported-by: Xiumei Mu <xmu@...hat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
---
 kernel/bpf/cpumap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 70f71b154fa5..23902afb3bba 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -99,8 +99,8 @@ static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
 
 	bpf_map_init_from_attr(&cmap->map, attr);
 
-	/* Pre-limit array size based on NR_CPUS, not final CPU check */
-	if (cmap->map.max_entries > NR_CPUS) {
+	/* Pre-limit array size based on nr_cpumask_bits, not final CPU check */
+	if (cmap->map.max_entries > nr_cpumask_bits) {
 		err = -E2BIG;
 		goto free_cmap;
 	}
-- 
2.26.0