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[195.135.220.15]) by mx.google.com with ESMTPS id h46si3447527edb.49.2019.05.17.05.51.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 May 2019 05:51:35 -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 5E16BAF59; Fri, 17 May 2019 12:51:35 +0000 (UTC) Date: Fri, 17 May 2019 14:51:34 +0200 From: Michal Hocko To: Konstantin Khlebnikov Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, Oleg Nesterov Subject: Re: [PATCH] mm: use down_read_killable for locking mmap_sem in access_remote_vm Message-ID: <20190517125134.GE1825@dhcp22.suse.cz> References: <155790847881.2798.7160461383704600177.stgit@buzz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <155790847881.2798.7160461383704600177.stgit@buzz> 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 Wed 15-05-19 11:21:18, Konstantin Khlebnikov wrote: > This function is used by ptrace and proc files like /proc/pid/cmdline and > /proc/pid/environ. Return 0 (bytes read) if current task is killed. Please add an explanation about why this is OK (as explained in the follow up email). > Mmap_sem could be locked for a long time or forever if something wrong. > > Signed-off-by: Konstantin Khlebnikov Acked-by: Michal Hocko > --- > mm/memory.c | 4 +++- > mm/nommu.c | 3 ++- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 96f1d473c89a..2e6846d09023 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4348,7 +4348,9 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm, > void *old_buf = buf; > int write = gup_flags & FOLL_WRITE; > > - down_read(&mm->mmap_sem); > + if (down_read_killable(&mm->mmap_sem)) > + return 0; > + > /* ignore errors, just check how much was successfully transferred */ > while (len) { > int bytes, ret, offset; > diff --git a/mm/nommu.c b/mm/nommu.c > index b492fd1fcf9f..cad8fb34088f 100644 > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1791,7 +1791,8 @@ int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm, > struct vm_area_struct *vma; > int write = gup_flags & FOLL_WRITE; > > - down_read(&mm->mmap_sem); > + if (down_read_killable(&mm->mmap_sem)) > + return 0; > > /* the access must start within one of the target process's mappings */ > vma = find_vma(mm, addr); -- Michal Hocko SUSE Labs