From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763422AbZE1Ppx (ORCPT ); Thu, 28 May 2009 11:45:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757223AbZE1Ppo (ORCPT ); Thu, 28 May 2009 11:45:44 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:60236 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752621AbZE1Ppn (ORCPT ); Thu, 28 May 2009 11:45:43 -0400 To: Alan Stern Cc: James Bottomley , Hannes Reinecke , Kay Sievers , SCSI development list , Andrew Morton , Greg Kroah-Hartman , Kernel development list , Tejun Heo , Cornelia Huck , , "Eric W. Biederman" References: From: ebiederm@xmission.com (Eric W. Biederman) Date: Thu, 28 May 2009 08:45:32 -0700 In-Reply-To: (Alan Stern's message of "Thu\, 28 May 2009 11\:24\:05 -0400 \(EDT\)") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=76.21.114.89;;;frm=ebiederm@xmission.com;;;spf=neutral X-SA-Exim-Connect-IP: 76.21.114.89 X-SA-Exim-Rcpt-To: stern@rowland.harvard.edu, ebiederm@aristanetworks.com, linux-fsdevel@vger.kernel.org, cornelia.huck@de.ibm.com, tj@kernel.org, linux-kernel@vger.kernel.org, gregkh@suse.de, akpm@linux-foundation.org, linux-scsi@vger.kernel.org, kay.sievers@vrfy.org, hare@suse.de, James.Bottomley@HansenPartnership.com X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Alan Stern X-Spam-Relay-Country: X-Spam-Report: * -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -0.7 BAYES_20 BODY: Bayesian spam probability is 5 to 20% * [score: 0.1229] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_TooManySym_01 4+ unique symbols in subject * 0.1 XMSolicitRefs_0 Weightloss drug * 0.0 XM_SPF_Neutral SPF-Neutral * 0.4 UNTRUSTED_Relay Comes from a non-trusted relay Subject: Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs directories. X-SA-Exim-Version: 4.2.1 (built Thu, 25 Oct 2007 00:26:12 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alan Stern writes: > There's another point to consider. If you do accept my argument that > empty targets can be removed from visibility regardless of the host's > state, then this removal races with addition of a new child. Since > removal involves calling device_del(), it can't be protected by the > host lock. Instead we'd have to use a mutex to protect both target > addition and target removal. Careful. Holding a lock over device_del is an easy and hidden way to trigger a rare deadlocks. Eric From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs directories. Date: Thu, 28 May 2009 08:45:32 -0700 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from out02.mta.xmission.com ([166.70.13.232]:60236 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752621AbZE1Ppn (ORCPT ); Thu, 28 May 2009 11:45:43 -0400 In-Reply-To: (Alan Stern's message of "Thu\, 28 May 2009 11\:24\:05 -0400 \(EDT\)") Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Alan Stern Cc: James Bottomley , Hannes Reinecke , Kay Sievers , SCSI development list , Andrew Morton , Greg Kroah-Hartman , Kernel development list , Tejun Heo , Cornelia Huck , linux-fsdevel@vger.kernel.org, "Eric W. Biederman" Alan Stern writes: > There's another point to consider. If you do accept my argument that > empty targets can be removed from visibility regardless of the host's > state, then this removal races with addition of a new child. Since > removal involves calling device_del(), it can't be protected by the > host lock. Instead we'd have to use a mutex to protect both target > addition and target removal. Careful. Holding a lock over device_del is an easy and hidden way to trigger a rare deadlocks. Eric