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[84.3.50.134]) by smtp.gmail.com with ESMTPSA id qn10sm3794945ejb.39.2020.07.27.04.43.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jul 2020 04:43:05 -0700 (PDT) Date: Mon, 27 Jul 2020 13:43:03 +0200 From: Ingo Molnar To: Muchun Song Cc: peterz@infradead.org, tglx@linutronix.de, bigeasy@linutronix.de, namit@vmware.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] smp: Fix a potential usage of stale nr_cpus Message-ID: <20200727114303.GA57241@gmail.com> References: <20200721034239.72013-1-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200721034239.72013-1-songmuchun@bytedance.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Muchun Song wrote: > When the cmdline of "nr_cpus" is not valid, the @nr_cpu_ids is assigned > a stale value. The nr_cpus is only valid when get_option() return 1. So > check the return value to prevent this. > > Signed-off-by: Muchun Song > --- > changelog in v3: > 1) Return -EINVAL when the parameter is bogus. > > changelog in v2: > 1) Rework the commit log. > 2) Rework the return value check. > > kernel/smp.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/smp.c b/kernel/smp.c > index a5a66fc28f4e..0dacfcfcf00b 100644 > --- a/kernel/smp.c > +++ b/kernel/smp.c > @@ -772,9 +772,13 @@ static int __init nrcpus(char *str) > { > int nr_cpus; > > - get_option(&str, &nr_cpus); > + if (get_option(&str, &nr_cpus) != 1) > + return -EINVAL; > + > if (nr_cpus > 0 && nr_cpus < nr_cpu_ids) > nr_cpu_ids = nr_cpus; > + else > + return -EINVAL; Exactly what does 'not valid' mean, and why doesn't get_option() return -EINVAL in that case? Thanks, Ingo