From mboxrd@z Thu Jan 1 00:00:00 1970 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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 C749FC11D2A for ; Mon, 24 Feb 2020 09:47:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A70D720838 for ; Mon, 24 Feb 2020 09:47:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727275AbgBXJrF (ORCPT ); Mon, 24 Feb 2020 04:47:05 -0500 Received: from mx2.suse.de ([195.135.220.15]:34338 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726628AbgBXJrF (ORCPT ); Mon, 24 Feb 2020 04:47:05 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 346BAAE64; Mon, 24 Feb 2020 09:47:02 +0000 (UTC) From: Vlastimil Babka To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka , Gerald Schaefer , Qian Cai , Joonsoo Kim , stable@vger.kernel.org Subject: [PATCH] mm, hotplug: fix page online with DEBUG_PAGEALLOC compiled but not enabled Date: Mon, 24 Feb 2020 10:46:51 +0100 Message-Id: <20200224094651.18257-1-vbabka@suse.cz> X-Mailer: git-send-email 2.25.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") fixed memory hotplug with debug_pagealloc enabled, where onlining a page goes through page freeing, which removes the direct mapping. Some arches don't like when the page is not mapped in the first place, so generic_online_page() maps it first. This is somewhat wasteful, but better than special casing page freeing fast paths. The commit however missed that DEBUG_PAGEALLOC configured doesn't mean it's actually enabled. One has to test debug_pagealloc_enabled() since 031bc5743f15 ("mm/debug-pagealloc: make debug-pagealloc boottime configurable"), or alternatively debug_pagealloc_enabled_static() since 8e57f8acbbd1 ("mm, debug_pagealloc: don't rely on static keys too early"), but this is not done. As a result, a s390 kernel with DEBUG_PAGEALLOC configured but not enabled will crash: Unable to handle kernel pointer dereference in virtual kernel address space Failing address: 0000000000000000 TEID: 0000000000000483 Fault in home space mode while using kernel ASCE. AS:0000001ece13400b R2:000003fff7fd000b R3:000003fff7fcc007 S:000003fff7fd7000 P:000000000000013d Oops: 0004 ilc:2 [#1] SMP CPU: 1 PID: 26015 Comm: chmem Kdump: loaded Tainted: GX 5.3.18-5-default #1 SLE15-SP2 (unreleased) Krnl PSW : 0704e00180000000 0000001ecd281b9e (__kernel_map_pages+0x166/0x188) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 Krnl GPRS: 0000000000000000 0000000000000800 0000400b00000000 0000000000000100 0000000000000001 0000000000000000 0000000000000002 0000000000000100 0000001ece139230 0000001ecdd98d40 0000400b00000100 0000000000000000 000003ffa17e4000 001fffe0114f7d08 0000001ecd4d93ea 001fffe0114f7b20 Krnl Code: 0000001ecd281b8e: ec17ffff00d8 ahik %r1,%r7,-1 0000001ecd281b94: ec111dbc0355 risbg %r1,%r1,29,188,3 >0000001ecd281b9e: 94fb5006 ni 6(%r5),251 0000001ecd281ba2: 41505008 la %r5,8(%r5) 0000001ecd281ba6: ec51fffc6064 cgrj %r5,%r1,6,1ecd281b9e 0000001ecd281bac: 1a07 ar %r0,%r7 0000001ecd281bae: ec03ff584076 crj %r0,%r3,4,1ecd281a5e Call Trace: [<0000001ecd281b9e>] __kernel_map_pages+0x166/0x188 [<0000001ecd4d9516>] online_pages_range+0xf6/0x128 [<0000001ecd2a8186>] walk_system_ram_range+0x7e/0xd8 [<0000001ecda28aae>] online_pages+0x2fe/0x3f0 [<0000001ecd7d02a6>] memory_subsys_online+0x8e/0xc0 [<0000001ecd7add42>] device_online+0x5a/0xc8 [<0000001ecd7d0430>] state_store+0x88/0x118 [<0000001ecd5b9f62>] kernfs_fop_write+0xc2/0x200 [<0000001ecd5064b6>] vfs_write+0x176/0x1e0 [<0000001ecd50676a>] ksys_write+0xa2/0x100 [<0000001ecda315d4>] system_call+0xd8/0x2c8 Fix this by checking debug_pagealloc_enabled_static() before calling kernel_map_pages(). Backports for kernel before 5.5 should use debug_pagealloc_enabled() instead. Also add comments. Fixes: cd02cf1aceea ("mm/hotplug: fix an imbalance with DEBUG_PAGEALLOC") Signed-off-by: Vlastimil Babka Reported-by: Gerald Schaefer Cc: Qian Cai Cc: Joonsoo Kim Cc: --- include/linux/mm.h | 4 ++++ mm/memory_hotplug.c | 8 +++++++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git include/linux/mm.h include/linux/mm.h index 52269e56c514..c54fb96cb1e6 100644 --- include/linux/mm.h +++ include/linux/mm.h @@ -2715,6 +2715,10 @@ static inline bool debug_pagealloc_enabled_static(void) #if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) extern void __kernel_map_pages(struct page *page, int numpages, int enable); +/* + * When called in DEBUG_PAGEALLOC context, the call should most likely be + * guarded by debug_pagealloc_enabled() or debug_pagealloc_enabled_static() + */ static inline void kernel_map_pages(struct page *page, int numpages, int enable) { diff --git mm/memory_hotplug.c mm/memory_hotplug.c index 0a54ffac8c68..19389cdc16a5 100644 --- mm/memory_hotplug.c +++ mm/memory_hotplug.c @@ -574,7 +574,13 @@ EXPORT_SYMBOL_GPL(restore_online_page_callback); void generic_online_page(struct page *page, unsigned int order) { - kernel_map_pages(page, 1 << order, 1); + /* + * Freeing the page with debug_pagealloc enabled will try to unmap it, + * so we should map it first. This is better than introducing a special + * case in page freeing fast path. + */ + if (debug_pagealloc_enabled_static()) + kernel_map_pages(page, 1 << order, 1); __free_pages_core(page, order); totalram_pages_add(1UL << order); #ifdef CONFIG_HIGHMEM -- 2.25.0