From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752155AbcFUOvS (ORCPT ); Tue, 21 Jun 2016 10:51:18 -0400 Received: from mail-lf0-f67.google.com ([209.85.215.67]:36415 "EHLO mail-lf0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751396AbcFUOvN (ORCPT ); Tue, 21 Jun 2016 10:51:13 -0400 Date: Tue, 21 Jun 2016 16:37:31 +0200 From: Michal Hocko To: zhongjiang Cc: akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Subject: Re: [PATCH] mm/huge_memory: fix the memory leak due to the race Message-ID: <20160621143731.GH30848@dhcp22.suse.cz> References: <1466517956-13875-1-git-send-email-zhongjiang@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1466517956-13875-1-git-send-email-zhongjiang@huawei.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [CCing Kirill] On Tue 21-06-16 22:05:56, zhongjiang wrote: > From: zhong jiang > > with great pressure, I run some test cases. As a result, I found > that the THP is not freed, it is detected by check_mm(). > > BUG: Bad rss-counter state mm:ffff8827edb70000 idx:1 val:512 > > Consider the following race : > > CPU0 CPU1 > __handle_mm_fault() > wp_huge_pmd() > do_huge_pmd_wp_page() > pmdp_huge_clear_flush_notify() > (pmd_none = true) > exit_mmap() > unmap_vmas() > zap_pmd_range() > pmd_none_or_trans_huge_or_clear_bad() > (result in memory leak) > set_pmd_at() > > because of CPU0 have allocated huge page before pmdp_huge_clear_notify, > and it make the pmd entry to be null. Therefore, The memory leak can occur. I do not understand this description. CPU1 is in the exit path with last mm user gone. So CPU0 is a different process with its own mm. How can they influence each other. But maybe I am just missing your point. > The patch fix the scenario that the pmd entry can lead to be null. > > Signed-off-by: zhong jiang > --- > mm/huge_memory.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index e10a4fe..ef04b94 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1340,11 +1340,11 @@ alloc: > pmd_t entry; > entry = mk_huge_pmd(new_page, vma->vm_page_prot); > entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); > - pmdp_huge_clear_flush_notify(vma, haddr, pmd); > + pmdp_invalidate(vma, haddr, pmd); > page_add_new_anon_rmap(new_page, vma, haddr, true); > mem_cgroup_commit_charge(new_page, memcg, false, true); > lru_cache_add_active_or_unevictable(new_page, vma); > - set_pmd_at(mm, haddr, pmd, entry); > + pmd_populate(mm, pmd, entry); > update_mmu_cache_pmd(vma, address, pmd); > if (!page) { > add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR); > -- > 1.8.3.1 -- Michal Hocko SUSE Labs