Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755382Ab0LQAyi (ORCPT ); Thu, 16 Dec 2010 19:54:38 -0500 Received: from smtp-out.google.com ([216.239.44.51]:10357 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754882Ab0LQAyf convert rfc822-to-8bit (ORCPT ); Thu, 16 Dec 2010 19:54:35 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=H/9d99awoo0lFUEz6II/O9wbmS8Zr+2WJCVseU/lU+9C7SiNBUFBaAFdn/TpCngYyY cJxX+UyFRmYlU5C6yyeg== MIME-Version: 1.0 In-Reply-To: References: <1290577024-12347-1-git-send-email-ccross@android.com> From: Paul Menage Date: Thu, 16 Dec 2010 16:54:09 -0800 Message-ID: Subject: Re: [PATCH 1/2] cgroup: Set CGRP_RELEASABLE when adding to a cgroup To: Colin Cross Cc: Li Zefan , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1453 Lines: 27 On Thu, Dec 2, 2010 at 7:07 PM, Colin Cross wrote: >> Not in one case - if we create a new cgroup and try to move a thread >> into it, but the thread is exiting as we move it, we'll call >> put_css_set() on the new css_set, which will drop the refcount on the >> target cgroup back to 0. We wouldn't want the auto-release >> notification to kick in in that situation, I think. > > Clearing the CGRP_RELEASABLE bit any time after the tests in > check_for_release introduces a race if __css_get is called between the > check and clearing the bit - the cgroup will have an entry, but the > bit will not be set. ?Without additional locking in __css_get, I don't > see any way to safely clear CGRP_RELEASABLE. I don't quite follow your argument here. Are you saying that the problem is that you could end up spawning a release agent for a cgroup that was no longer releasable since it now had a process in it again? If so, then I don't think that's a problem - spurious release agent invocations for non-empty cgroups will always happen occasionally due to races between the kernel and userspace. But a failed move of a task into a previously-empty cgroup shouldn't trigger the agent. Paul -- 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/