From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753280Ab0ELNL7 (ORCPT ); Wed, 12 May 2010 09:11:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:29981 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751565Ab0ELNL5 (ORCPT ); Wed, 12 May 2010 09:11:57 -0400 Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <1273634462-2672-13-git-send-email-walken@google.com> References: <1273634462-2672-13-git-send-email-walken@google.com> <1273634462-2672-1-git-send-email-walken@google.com> To: Michel Lespinasse Cc: dhowells@redhat.com, Linus Torvalds , Ingo Molnar , Thomas Gleixner , LKML , Andrew Morton , Mike Waychison , Suleiman Souhlal , Ying Han Subject: Re: [PATCH 12/12] Use down_read_unfair() for /sys//exe and /sys//maps files Date: Wed, 12 May 2010 14:10:38 +0100 Message-ID: <10175.1273669838@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Michel Lespinasse wrote: > - Thread C is a monitoring process trying to read every /proc/pid/maps > in the system. This requires acquiring the mmap_sem for read. Thread C > blocks behind B, waiting for A to release the rwsem. If thread C > could be allowed to run in parallel with A, it would probably get done > long before thread A's disk access completes, thus not actually slowing > down thread B. Is it possible for someone to execute a DoS attack on another process using a bunch of threads reading /proc/pid/maps? David