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[209.85.220.65]) by mx.google.com with SMTPS id b26sor811554lfa.36.2019.04.18.11.23.23 for (Google Transport Security); Thu, 18 Apr 2019 11:23:23 -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=oCZtbd8w; 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=vC2agpd/yeTIjkC+tv6Q0HWjOpOqDC0mbvCHm0eBf4Y=; b=oCZtbd8wbvAsIKhSYoUJZQVeVFzI9LhVk5xw5A9aYv70oTCxPDa6CUjfhq+7Ko97Yw 5EBuW7fdsXGgA4duhAS6WpIwtYcQqgAk9n2TFWUG9A7Guuq6Wjh96ylkUMKabdIy43a6 8DlL8MSTSorKUkzsLvIHVbj17K+BG/zixxqBZhZOCrrzOYOTMKXRFKWY3xzHa5FX0FnE N6PJsM8S5vsd0FFiKD5cO1kUvacWe5/8AigkrFKVHcH1e2gmueli4YEM7P5c4pgH8ojH IXmHDGo8zSl1fe/FBh+n8Fy+4L+B3KeT+Qf9JY48R+SfJhpOvzSGNTMAIWBWK6bhaoHX t7lA== X-Google-Smtp-Source: APXvYqyBjDf0Lb5iqi1H4sy3SWYyTORWzsqfNAlBTaJ1dtcbk6DdNBZyJ36/uSTPPp/2Mrwa4eR7NA== X-Received: by 2002:a19:c51a:: with SMTP id w26mr50367270lfe.59.1555611802703; Thu, 18 Apr 2019 11:23:22 -0700 (PDT) Received: from uranus.localdomain ([5.18.103.226]) by smtp.gmail.com with ESMTPSA id n28sm90162lfi.79.2019.04.18.11.23.21 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 18 Apr 2019 11:23:22 -0700 (PDT) Received: by uranus.localdomain (Postfix, from userid 1000) id B8D49460E21; Thu, 18 Apr 2019 21:23:21 +0300 (MSK) Date: Thu, 18 Apr 2019 21:23:21 +0300 From: Cyrill Gorcunov To: Michal =?iso-8859-1?Q?Koutn=FD?= Cc: mhocko@kernel.org, akpm@linux-foundation.org, arunks@codeaurora.org, brgl@bgdev.pl, geert+renesas@glider.be, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mguzik@redhat.com, rppt@linux.ibm.com, vbabka@suse.cz, Laurent Dufour Subject: Re: [PATCH] prctl_set_mm: downgrade mmap_sem to read lock Message-ID: <20190418182321.GJ3040@uranus.lan> References: <20190417145548.GN5878@dhcp22.suse.cz> <20190418135039.19987-1-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: <20190418135039.19987-1-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, Apr 18, 2019 at 03:50:39PM +0200, Michal Koutný wrote: > I learnt, it's, alas, too late to drop the non PRCTL_SET_MM_MAP calls > [1], so at least downgrade the write acquisition of mmap_sem as in the > patch below (that should be stacked on the previous one or squashed). > > Cyrill, you mentioned lock changes in [1] but the link seems empty. Is > it supposed to be [2]? That could be an alternative to this patch after > some refreshments and clarifications. > > > [1] https://lore.kernel.org/lkml/20190417165632.GC3040@uranus.lan/ > [2] https://lore.kernel.org/lkml/20180507075606.870903028@gmail.com/ > > ======== > > Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect > arg_start|end and env_start|end in mm_struct") we use arg_lock for > boundaries modifications. Synchronize prctl_set_mm with this lock and > keep mmap_sem for reading only (analogous to what we already do in > prctl_set_mm_map). > > Also, save few cycles by looking up VMA only after performing basic > arguments validation. > > Signed-off-by: Michal Koutný Reviewed-by: Cyrill Gorcunov As Laurent mentioned we might move vma lookup before the spinlock, but this might be done on top of the series.