From patchwork Sat Aug 22 17:30:05 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 265217 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0F460C433DF for ; Sat, 22 Aug 2020 17:30:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E5D5A20724 for ; Sat, 22 Aug 2020 17:30:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598117417; bh=elCfwKD63LtrrZCV7YkE1z0OdQ3yq9adXZbbT7ILSbA=; h=Date:From:To:Subject:List-ID:From; b=HKiyPxQwVprWw9vH/zlB7vDzdC2nqN2+guwLUE0B6Pg0CsCvz0dVKxWxADMFOKM33 0eYR/xnQ9Z33jlJkehWT3JM5/EqYJH/VG2B3b+8a4zaQCYSq5tXoHvXQYSG7IgC9SX QsNSUTeBwX6GqolQC1PlA/mjCFmxR4zS2XDe9rMo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728401AbgHVRaQ (ORCPT ); Sat, 22 Aug 2020 13:30:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:54074 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728417AbgHVRaG (ORCPT ); Sat, 22 Aug 2020 13:30:06 -0400 Received: from localhost.localdomain (c-71-198-47-131.hsd1.ca.comcast.net [71.198.47.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6BC26214F1; Sat, 22 Aug 2020 17:30:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598117405; bh=elCfwKD63LtrrZCV7YkE1z0OdQ3yq9adXZbbT7ILSbA=; h=Date:From:To:Subject:From; b=EyirHYcNcgB6sayNe3Qp0mCJnv5eASOcaAlzKEYSYN9TUO/qlqXmwqdkmTNtBg6tC ZvFIWvNZG9Q6R7Ed2Lkmn2CKqdVjddKCJyRE1liDiF0UXGg8nUJHdyPvmlUramG4JO Zh3PqpMjKM+Q+NmKbOPdZQAoLQaq5a/wfdLz1PJU= Date: Sat, 22 Aug 2020 10:30:05 -0700 From: akpm@linux-foundation.org To: charante@codeaurora.org, david@redhat.com, mhocko@suse.com, mm-commits@vger.kernel.org, rientjes@google.com, stable@vger.kernel.org, vbabka@suse.cz, vinmenon@codeaurora.org Subject: [merged] mm-page_alloc-fix-core-hung-in-free_pcppages_bulk.patch removed from -mm tree Message-ID: <20200822173005.iUjGe5PXk%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: mm, page_alloc: fix core hung in free_pcppages_bulk() has been removed from the -mm tree. Its filename was mm-page_alloc-fix-core-hung-in-free_pcppages_bulk.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Charan Teja Reddy Subject: mm, page_alloc: fix core hung in free_pcppages_bulk() The following race is observed with the repeated online, offline and a delay between two successive online of memory blocks of movable zone. P1 P2 Online the first memory block in the movable zone. The pcp struct values are initialized to default values,i.e., pcp->high = 0 & pcp->batch = 1. Allocate the pages from the movable zone. Try to Online the second memory block in the movable zone thus it entered the online_pages() but yet to call zone_pcp_update(). This process is entered into the exit path thus it tries to release the order-0 pages to pcp lists through free_unref_page_commit(). As pcp->high = 0, pcp->count = 1 proceed to call the function free_pcppages_bulk(). Update the pcp values thus the new pcp values are like, say, pcp->high = 378, pcp->batch = 63. Read the pcp's batch value using READ_ONCE() and pass the same to free_pcppages_bulk(), pcp values passed here are, batch = 63, count = 1. Since num of pages in the pcp lists are less than ->batch, then it will stuck in while(list_empty(list)) loop with interrupts disabled thus a core hung. Avoid this by ensuring free_pcppages_bulk() is called with proper count of pcp list pages. The mentioned race is some what easily reproducible without [1] because pcp's are not updated for the first memory block online and thus there is a enough race window for P2 between alloc+free and pcp struct values update through onlining of second memory block. With [1], the race still exists but it is very narrow as we update the pcp struct values for the first memory block online itself. This is not limited to the movable zone, it could also happen in cases with the normal zone (e.g., hotplug to a node that only has DMA memory, or no other memory yet). [1]: https://patchwork.kernel.org/patch/11696389/ Link: http://lkml.kernel.org/r/1597150703-19003-1-git-send-email-charante@codeaurora.org Fixes: 5f8dcc21211a ("page-allocator: split per-cpu list into one-list-per-migrate-type") Signed-off-by: Charan Teja Reddy Acked-by: David Hildenbrand Acked-by: David Rientjes Acked-by: Michal Hocko Cc: Michal Hocko Cc: Vlastimil Babka Cc: Vinayak Menon Cc: [2.6+] Signed-off-by: Andrew Morton --- mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/mm/page_alloc.c~mm-page_alloc-fix-core-hung-in-free_pcppages_bulk +++ a/mm/page_alloc.c @@ -1302,6 +1302,11 @@ static void free_pcppages_bulk(struct zo struct page *page, *tmp; LIST_HEAD(head); + /* + * Ensure proper count is passed which otherwise would stuck in the + * below while (list_empty(list)) loop. + */ + count = min(pcp->count, count); while (count) { struct list_head *list;