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From: Roman Gushchin To: Yafang Shao Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, hannes@cmpxchg.org, mhocko@kernel.org, shakeelb@google.com, songmuchun@bytedance.com, akpm@linux-foundation.org, netdev@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH bpf-next 05/15] bpf: Fix incorrect mem_cgroup_put Message-ID: References: <20220810151840.16394-1-laoar.shao@gmail.com> <20220810151840.16394-6-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220810151840.16394-6-laoar.shao@gmail.com> X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660236538; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=9LRo2B5nHj7qM/j+ODxu8goN8T5MUtYCM7InUsCq2KI=; b=5yQV/ug2DfZG/nD/WyNKxMMmyltXUFDsFIobFkpiE5uJFKg6cT25HUBD8LumS8Dnc9aM2I bJSNYLHrkVCsYol8QoDwGr7MxRLBmdNtGiLZyyMQ5Eo2uWvpbtlgo3wV9EM+Zes4e26GZa B9lUJgbFA+4azsnUE7PssNbwfpcNmkY= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=QrHjuwkW; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf17.hostedemail.com: domain of roman.gushchin@linux.dev designates 188.165.223.204 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660236538; a=rsa-sha256; cv=none; b=53rfmhwH/fQNt/cD96LWrOOBiVzy77E1Az25c2yfTKL8Ef59mKpjXgCdVJr9a6sITFcFrL 7EWXAHa3j60bUp3bYKNKojg9MgOaKdIh08cVb0J9CrSSwoe/9BeR8JL4OzKkjX1Hzxgmng OdqHXDSyfo6de3nk8tAruTOddwqB6sg= X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A478B40065 X-Rspam-User: X-Stat-Signature: yuhdg19gmya4e1hfgjge8xys1zuttiy3 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=QrHjuwkW; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf17.hostedemail.com: domain of roman.gushchin@linux.dev designates 188.165.223.204 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev X-HE-Tag: 1660236537-549931 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Aug 10, 2022 at 03:18:30PM +0000, Yafang Shao wrote: > The memcg may be the root_mem_cgroup, in which case we shouldn't put it. > So a new helper bpf_map_put_memcg() is introduced to pair with > bpf_map_get_memcg(). > > Fixes: 4201d9ab3e42 ("bpf: reparent bpf maps on memcg offlining") > Cc: Roman Gushchin > Cc: Shakeel Butt > Signed-off-by: Yafang Shao > --- > kernel/bpf/syscall.c | 14 +++++++++++--- > 1 file changed, 11 insertions(+), 3 deletions(-) > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 83c7136..51ab8b1 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -441,6 +441,14 @@ static struct mem_cgroup *bpf_map_get_memcg(const struct bpf_map *map) > return root_mem_cgroup; > } > > +static void bpf_map_put_memcg(struct mem_cgroup *memcg) > +{ > + if (mem_cgroup_is_root(memcg)) > + return; > + > + mem_cgroup_put(memcg); > +} +1 to what Shakeel said. mem_cgroup_put(root_mem_cgroup) is totally valid. So this change does absolutely nothing. The fixes tag assumes there is a bug in the existing code. If so, please, describe the problem and how to reproduce it. Also, if it's not related to the rest of the patchset, please, send it separately. Thanks!