From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935828Ab3BTU2m (ORCPT ); Wed, 20 Feb 2013 15:28:42 -0500 Received: from out03.mta.xmission.com ([166.70.13.233]:42329 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934793Ab3BTU2l (ORCPT ); Wed, 20 Feb 2013 15:28:41 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Alan Stern Cc: Li Fei , , , , , , , , , , , , , References: Date: Wed, 20 Feb 2013 12:28:12 -0800 In-Reply-To: (Alan Stern's message of "Wed, 20 Feb 2013 10:24:12 -0500 (EST)") Message-ID: <87obfeivc3.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1/MqmBapiZK+3gGkhkvYZXJdvqhkenDyUo= X-SA-Exim-Connect-IP: 98.207.153.68 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.1 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa03 1397; Body=1 Fuz1=1 Fuz2=1] * 0.0 T_XMDrugObfuBody_14 obfuscated drug references X-Spam-DCC: XMission; sa03 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Alan Stern X-Spam-Relay-Country: Subject: Re: [PATCH] freezer: configure user space process frozen along with kernel threads X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Wed, 14 Nov 2012 14:26:46 -0700) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Alan Stern writes: > On Wed, 20 Feb 2013, Eric W. Biederman wrote: > >> Why can't the fuse filesystem freeze when there are requests pending? > > It _can_ freeze (that is, the fuse daemon can). The problem is that > tasks _using_ the fuse filsystem can't if the daemon doesn't respond. Which is what I meant when I said that the fuse filesystem couldn't freeze. > These tasks are stuck in uninterruptible wait states deep in the > filesystem layer, probably holding important locks. They can't be > frozen until the outstanding requests complete. Why is it that processes that can be preempted can't be frozen? At most I would suggest that processes be frozen in reverse priority order. Which unless there is a priority inversion should solve this problem without an additional proc file. Adding a userspace interface that doesn't come close to doing the right thing automatically and that is brittle and will likely fail in ways even stranger and harder to track ways than fuse is failing today seems like totally the wrong direction to go. Not adding any permission checks to the proc files just compounds the problem. Eric