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[209.85.220.65]) by mx.google.com with SMTPS id w4sor14743687pfi.67.2019.05.27.16.33.14 for (Google Transport Security); Mon, 27 May 2019 16:33:14 -0700 (PDT) Received-SPF: pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=Pcm1ooQR; spf=pass (google.com: domain of minchan.kim@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=minchan.kim@gmail.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=+Tzevj0aBFVFkJCWK4eLpOvzUlkBo2BfRqQfZEvwMvs=; b=Pcm1ooQR7nJPiwEsinFV/L6nU72jYejpbNC7QlSuOh8Pr/Z7jHPUQy9LUaDpG3ZZiM +y0KLQUxNoHblKkmwGb+K2LT3jNmHSweUA8KOn53jFvOagl8BB01uHMmr4Urgm7G7kzD i9oE0PzDFV3dp3p4jzFvhv08fTGoOAyudo4yFzXQ/AYO1FA/npUwnQLAk0eTJe8aRySd xpHXTeOT1+LNS9vzNUHPyk3kEzHbL8xv+pWQfDUV7yC6yNTdtI7zVh6xRdi56muGJLNV vrxlxGW79TUzoRd+V1xYEHmU+3m+Re5rThIDKwi1R9C/6KzcnUuFWJPjFMXqnM9HA3Tt aC1Q== X-Google-Smtp-Source: APXvYqw64MwbF8rBzoFZuNCZfbyzEPvHcK3q4MMq9vzVc16EWSgge+/RGsYDd+RrqQ/wO+LlCjxZUw== X-Received: by 2002:a62:d41c:: with SMTP id a28mr40306175pfh.31.1558999993555; Mon, 27 May 2019 16:33:13 -0700 (PDT) Received: from google.com ([2401:fa00:d:0:98f1:8b3d:1f37:3e8]) by smtp.gmail.com with ESMTPSA id n2sm10802478pgp.27.2019.05.27.16.33.09 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 27 May 2019 16:33:12 -0700 (PDT) Date: Tue, 28 May 2019 08:33:06 +0900 From: Minchan Kim To: Oleg Nesterov Cc: Andrew Morton , LKML , linux-mm , Michal Hocko , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon Subject: Re: [RFC 5/7] mm: introduce external memory hinting API Message-ID: <20190527233306.GE6879@google.com> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-6-minchan@kernel.org> <20190521153113.GA2235@redhat.com> <20190527074300.GA6879@google.com> <20190527151201.GB8961@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190527151201.GB8961@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 Mon, May 27, 2019 at 05:12:02PM +0200, Oleg Nesterov wrote: > On 05/27, Minchan Kim wrote: > > > > > another problem is that pid_task(pid) can return a zombie leader, in this case > > > mm_access() will fail while it shouldn't. > > > > I'm sorry. I didn't notice that. However, I couldn't understand your point. > > Why do you think mm_access shouldn't fail even though pid_task returns > > a zombie leader? > > The leader can exit (call sys_exit(), not sys_exit_group()), this won't affect > other threads. In this case the process is still alive even if the leader thread > is zombie. That is why we have find_lock_task_mm(). Thanks for clarification, Oleg. Then, Let me have a further question. It means process_vm_readv, move_pages have same problem too because find_task_by_vpid can return a zomebie leader and next line checks for mm_struct validation makes a failure. My understand is correct? If so, we need to fix all places.