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[195.135.220.15]) by mx.google.com with ESMTPS id n12si10196500ejr.105.2019.06.18.22.18.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 18 Jun 2019 22:18:09 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 80758ADF7; Wed, 19 Jun 2019 05:18:08 +0000 (UTC) Date: Wed, 19 Jun 2019 07:18:05 +0200 From: Michal Hocko To: Andrea Arcangeli Cc: Andrew Morton , linux-mm@kvack.org, Rik van Riel , Roman Gushchin Subject: Re: [PATCH 1/1] fork,memcg: alloc_thread_stack_node needs to set tsk->stack Message-ID: <20190619051805.GA2968@dhcp22.suse.cz> References: <20190619011450.28048-1-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190619011450.28048-1-aarcange@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 Tue 18-06-19 21:14:50, Andrea Arcangeli wrote: > Commit 5eed6f1dff87bfb5e545935def3843edf42800f2 corrected two > instances, but there was a third instance of this bug. Sigh. I should have noticed when reviewing the above. My bad. > Without setting tsk->stack, if memcg_charge_kernel_stack fails, it'll > execute free_thread_stack() on a dangling pointer. > > Enterprise kernels are compiled with VMAP_STACK=y so this isn't > critical, but custom VMAP_STACK=n builds should have some performance > advantage, with the drawback of risking to fail fork because > compaction didn't succeed. So as long as VMAP_STACK=n is a supported > option it's worth fixing it upstream. > > Fixes: 9b6f7e163cd0 ("mm: rework memcg kernel stack accounting") > Signed-off-by: Andrea Arcangeli Acked-by: Michal Hocko I have double checked now and it seems we have covered all the cases finally. Thanks! > --- > kernel/fork.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index d6c324b1b29e..9ee28dfe7c21 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -248,7 +248,11 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) > struct page *page = alloc_pages_node(node, THREADINFO_GFP, > THREAD_SIZE_ORDER); > > - return page ? page_address(page) : NULL; > + if (likely(page)) { > + tsk->stack = page_address(page); > + return tsk->stack; > + } > + return NULL; > #endif > } > -- Michal Hocko SUSE Labs