Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755124Ab3CUEsk (ORCPT ); Thu, 21 Mar 2013 00:48:40 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:56751 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750836Ab3CUEsj (ORCPT ); Thu, 21 Mar 2013 00:48:39 -0400 MIME-Version: 1.0 In-Reply-To: <514A7E72.2090200@huawei.com> References: <1363793126-11510-1-git-send-email-ming.lei@canonical.com> <1363793126-11510-2-git-send-email-ming.lei@canonical.com> <514A7340.5040409@huawei.com> <514A7E72.2090200@huawei.com> Date: Thu, 21 Mar 2013 12:48:36 +0800 Message-ID: Subject: Re: [PATCH 1/2] sysfs: fix race between readdir and lseek From: Ming Lei To: Li Zefan Cc: Greg Kroah-Hartman , linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1416 Lines: 41 On Thu, Mar 21, 2013 at 11:28 AM, Li Zefan wrote: > On 2013/3/21 11:17, Ming Lei wrote: >> On Thu, Mar 21, 2013 at 10:41 AM, Li Zefan wrote: >>> >>> In fact the same race exists between readdir() and read()/write()... >> >> Fortunately, no read()/write() are implemented on sysfs directory, :-) >> > > That's irrelevant... As far as sysfs is concerned, the filp->f_ops can't be changed in read/write path. > > See my report: > > https://patchwork.kernel.org/patch/2160771/ Yes, I know there might be some mess after the commit ef3d0fd2 (vfs: do (nearly) lockless generic_file_llseek). Also looks it has been stated in Documentation/filesystems/Locking: ->llseek() locking has moved from llseek to the individual llseek implementations. If your fs is not using generic_file_llseek, you need to acquire and release the appropriate locks in your ->llseek(). For many filesystems, it is probably safe to acquire the inode mutex or just to use i_size_read() instead. Note: this does not protect the file->f_pos against concurrent modifications since this is something the userspace has to take care about. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/