From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx126.postini.com [74.125.245.126]) by kanga.kvack.org (Postfix) with SMTP id AF5F46B005C for ; Wed, 18 Jul 2012 22:55:21 -0400 (EDT) Received: from /spool/local by e23smtp09.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 19 Jul 2012 03:41:32 +1000 Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q6J2lBl659572430 for ; Thu, 19 Jul 2012 12:47:12 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q6J2tCF0025047 for ; Thu, 19 Jul 2012 12:55:12 +1000 From: "Aneesh Kumar K.V" Subject: Re: [PATCH] hugetlb/cgroup: Simplify pre_destroy callback In-Reply-To: <20120718142628.76bf78b3.akpm@linux-foundation.org> References: <1342589649-15066-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20120718142628.76bf78b3.akpm@linux-foundation.org> Date: Thu, 19 Jul 2012 08:25:06 +0530 Message-ID: <87hat4794l.fsf@skywalker.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, mhocko@suse.cz, linux-kernel@vger.kernel.org Andrew Morton writes: > On Wed, 18 Jul 2012 11:04:09 +0530 > "Aneesh Kumar K.V" wrote: > >> From: "Aneesh Kumar K.V" >> >> Since we cannot fail in hugetlb_cgroup_move_parent, we don't really >> need to check whether cgroup have any change left after that. Also skip >> those hstates for which we don't have any charge in this cgroup. >> >> ... >> >> + for_each_hstate(h) { >> + /* >> + * if we don't have any charge, skip this hstate >> + */ >> + idx = hstate_index(h); >> + if (res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE) == 0) >> + continue; >> + spin_lock(&hugetlb_lock); >> + list_for_each_entry(page, &h->hugepage_activelist, lru) >> + hugetlb_cgroup_move_parent(idx, cgroup, page); >> + spin_unlock(&hugetlb_lock); >> + VM_BUG_ON(res_counter_read_u64(&h_cg->hugepage[idx], RES_USAGE)); >> + } >> out: >> return ret; >> } > > This looks fishy. > > We test RES_USAGE before taking hugetlb_lock. What prevents some other > thread from increasing RES_USAGE after that test? > > After walking the list we test RES_USAGE after dropping hugetlb_lock. > What prevents another thread from incrementing RES_USAGE before that > test, triggering the BUG? IIUC core cgroup will prevent a new task getting added to the cgroup when we are in pre_destroy. Since we already check that the cgroup doesn't have any task, the RES_USAGE cannot increase in pre_destroy. -aneesh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org