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[209.85.220.65]) by mx.google.com with SMTPS id e10sor129600lfb.28.2019.05.02.13.57.36 for (Google Transport Security); Thu, 02 May 2019 13:57:36 -0700 (PDT) Received-SPF: pass (google.com: domain of gorcunov@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=deYS98jc; spf=pass (google.com: domain of gorcunov@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=gorcunov@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=pBJ9w6lgY/gbDSyW6tu8FbPiPrRqqN8hgCcI/ouWv4M=; b=deYS98jcrPo1YtSz5GL3B0iQfozu+v1yEvuPzAsdsWGhfbJyvv724RHPDCPBBUz193 YmuuZ+3J9FDyqp4UAwMQnt6Danwa/3aTV1V/HxcOnba0F5DXgFVk8oJcsWcEBkao3Wau TDnrwHrKm3VF+k3A+EikcEYFO60/XJVCPvWztbFMfjxcKEDbQ6O5UvIjRLKjAhTcKMeg gWN4c3Y6aFwxybH+m+zq+OulOAjA6Fi7S2F2PDtnO/K+i+CDvNMhWXzzp1X8VRuAkqXM 6ybTE89hB3ATBTkF4BitNCuLpA1YRtrkGikfV8/THNgtw6c/rGI9wxPDTBznvH9+NEkS 5m8Q== X-Google-Smtp-Source: APXvYqxpwSHaqM6yCkiO3Pu3fwtOtpblG0k9kQIfYRQCf8nihjcaltZKVv+2R0xqJFSn+bFWlEOiAQ== X-Received: by 2002:ac2:5307:: with SMTP id c7mr3062605lfh.58.1556830655847; Thu, 02 May 2019 13:57:35 -0700 (PDT) Received: from uranus.localdomain ([5.18.103.226]) by smtp.gmail.com with ESMTPSA id j9sm11251lja.92.2019.05.02.13.57.34 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 02 May 2019 13:57:34 -0700 (PDT) Received: by uranus.localdomain (Postfix, from userid 1000) id 4DA9D4603CA; Thu, 2 May 2019 23:57:34 +0300 (MSK) Date: Thu, 2 May 2019 23:57:34 +0300 From: Cyrill Gorcunov To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: akpm@linux-foundation.org, arunks@codeaurora.org, brgl@bgdev.pl, geert+renesas@glider.be, ldufour@linux.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mguzik@redhat.com, mhocko@kernel.org, rppt@linux.ibm.com, vbabka@suse.cz, ktkhai@virtuozzo.com Subject: Re: [PATCH v3 2/2] prctl_set_mm: downgrade mmap_sem to read lock Message-ID: <20190502205734.GE2488@uranus.lan> References: <0a48e0a2-a282-159e-a56e-201fbc0faa91@virtuozzo.com> <20190502125203.24014-1-mkoutny@suse.com> <20190502125203.24014-3-mkoutny@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190502125203.24014-3-mkoutny@suse.com> User-Agent: Mutt/1.11.3 (2019-02-01) 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 Thu, May 02, 2019 at 02:52:03PM +0200, Michal Koutný wrote: > The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap > semaphore taken.") added synchronization of reading argument/environment > boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce > arg_lock to protect arg_start|end and env_start|end in mm_struct") > avoided the coarse use of mmap_sem in similar situations. But there > still remained two places that (mis)use mmap_sem. > > get_cmdline should also use arg_lock instead of mmap_sem when it reads the > boundaries. > > The second place that should use arg_lock is in prctl_set_mm. By > protecting the boundaries fields with the arg_lock, we can downgrade > mmap_sem to reader lock (analogous to what we already do in > prctl_set_mm_map). > > v2: call find_vma without arg_lock held > v3: squashed get_cmdline arg_lock patch > > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") > Cc: Yang Shi > Cc: Mateusz Guzik > CC: Cyrill Gorcunov > Co-developed-by: Laurent Dufour > Signed-off-by: Laurent Dufour > Signed-off-by: Michal Koutný Reviewed-by: Cyrill Gorcunov