From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f198.google.com (mail-lb0-f198.google.com [209.85.217.198]) by kanga.kvack.org (Postfix) with ESMTP id 8F7BF828E1 for ; Tue, 21 Jun 2016 10:37:05 -0400 (EDT) Received: by mail-lb0-f198.google.com with SMTP id nq2so15869897lbc.3 for ; Tue, 21 Jun 2016 07:37:05 -0700 (PDT) Received: from mail-lf0-x243.google.com (mail-lf0-x243.google.com. [2a00:1450:4010:c07::243]) by mx.google.com with ESMTPS id m203si25776588lfb.181.2016.06.21.07.37.04 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 Jun 2016 07:37:04 -0700 (PDT) Received: by mail-lf0-x243.google.com with SMTP id l184so4041010lfl.1 for ; Tue, 21 Jun 2016 07:37:04 -0700 (PDT) Date: Tue, 21 Jun 2016 17:37:01 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mm/huge_memory: fix the memory leak due to the race Message-ID: <20160621143701.GA6139@node.shutemov.name> 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> Sender: owner-linux-mm@kvack.org List-ID: To: zhongjiang Cc: mhocko@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Jun 21, 2016 at 10:05:56PM +0800, 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. > > The patch fix the scenario that the pmd entry can lead to be null. I don't think the scenario is possible. exit_mmap() called when all mm users have gone, so no parallel threads exist. -- Kirill A. Shutemov -- 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