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[209.132.183.28]) by mx.google.com with ESMTPS id n94si2706266qte.210.2019.05.21.08.31.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 May 2019 08:31:27 -0700 (PDT) Received-SPF: pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of oleg@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=oleg@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9E2FC356F2; Tue, 21 May 2019 15:31:19 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.159]) by smtp.corp.redhat.com (Postfix) with SMTP id D8BD959154; Tue, 21 May 2019 15:31:14 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 21 May 2019 17:31:18 +0200 (CEST) Date: Tue, 21 May 2019 17:31:13 +0200 From: Oleg Nesterov To: Minchan Kim 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: <20190521153113.GA2235@redhat.com> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-6-minchan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190520035254.57579-6-minchan@kernel.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Tue, 21 May 2019 15:31:27 +0000 (UTC) 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 05/20, Minchan Kim wrote: > > + rcu_read_lock(); > + tsk = pid_task(pid, PIDTYPE_PID); > + if (!tsk) { > + rcu_read_unlock(); > + goto err; > + } > + get_task_struct(tsk); > + rcu_read_unlock(); > + mm = mm_access(tsk, PTRACE_MODE_ATTACH_REALCREDS); > + if (!mm || IS_ERR(mm)) { > + ret = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH; > + if (ret == -EACCES) > + ret = -EPERM; > + goto err; > + } > + ret = madvise_core(tsk, start, len_in, behavior); IIUC, madvise_core(tsk) plays with tsk->mm->mmap_sem. But this tsk can exit and nullify its ->mm right after mm_access() succeeds. another problem is that pid_task(pid) can return a zombie leader, in this case mm_access() will fail while it shouldn't. Oleg.