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[35.238.199.243]) by smtp.gmail.com with ESMTPSA id y27sm4849431iox.17.2021.06.18.11.20.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Jun 2021 11:20:02 -0700 (PDT) Date: Fri, 18 Jun 2021 18:20:01 +0000 From: Dennis Zhou To: Wan Jiabing Cc: Tejun Heo , Christoph Lameter , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kael_w@yeah.net Subject: Re: [PATCH] mm/percpu: Fix gfp flag in pcpu_balance_populated Message-ID: References: <20210618151436.38217-1-wanjiabing@vivo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210618151436.38217-1-wanjiabing@vivo.com> Authentication-Results: imf08.hostedemail.com; dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=kernel.org (policy=none); spf=pass (imf08.hostedemail.com: domain of dennisszhou@gmail.com designates 209.85.166.52 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com X-Stat-Signature: uphewtsc7uuxpm9zzmgg49ttfzf637mo X-Rspamd-Queue-Id: 9392F801934D X-Rspamd-Server: rspam06 X-HE-Tag: 1624040402-342967 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: Hello, On Fri, Jun 18, 2021 at 11:14:36PM +0800, Wan Jiabing wrote: > Fix coccicheck warning: > > ./mm/percpu.c:2045:19-29: ERROR: function pcpu_balance_populated > called on line 2232 inside lock on line 2228 but uses GFP_KERNEL > > When pcpu_balance_populated() is called in pcpu_balance_workfn(), > it helds spin_lock but use GFP_KERNEL to alloc mem, which is unsafe. > > Signed-off-by: Wan Jiabing > --- > mm/percpu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/percpu.c b/mm/percpu.c > index b4cebeca4c0c..4031f32e6975 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -2042,7 +2042,7 @@ static void pcpu_balance_free(bool empty_only) > static void pcpu_balance_populated(void) > { > /* gfp flags passed to underlying allocators */ > - const gfp_t gfp = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN; > + const gfp_t gfp = GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN; > struct pcpu_chunk *chunk; > int slot, nr_to_pop, ret; > > -- > 2.30.2 > In both places gfp flags are passed, the pcpu_lock is dropped. So I think this is an issue with coccicheck. Regardless, the fix wouldn't be to switch to GFP_ATOMIC but to make the locking correct. Thanks, Dennis