From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 130/155] mm, compaction: fully assume capture is not NULL in compact_zone_order() Date: Wed, 01 Apr 2020 21:10:35 -0700 Message-ID: <20200402041035.4VQwoAP_3%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:36276 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726136AbgDBEKg (ORCPT ); Thu, 2 Apr 2020 00:10:36 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, dan.carpenter@oracle.com, linux-mm@kvack.org, mgorman@techsingularity.net, mm-commits@vger.kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz From: Vlastimil Babka Subject: mm, compaction: fully assume capture is not NULL in compact_zone_order() Dan reports: The patch 5e1f0f098b46: "mm, compaction: capture a page under direct compaction" from Mar 5, 2019, leads to the following Smatch complaint: mm/compaction.c:2321 compact_zone_order() error: we previously assumed 'capture' could be null (see line 2313) mm/compaction.c 2288 static enum compact_result compact_zone_order(struct zone *zone, int order, 2289 gfp_t gfp_mask, enum compact_priority prio, 2290 unsigned int alloc_flags, int classzone_idx, 2291 struct page **capture) ^^^^^^^ 2313 if (capture) ^^^^^^^ Check for NULL 2314 current->capture_control = &capc; 2315 2316 ret = compact_zone(&cc, &capc); 2317 2318 VM_BUG_ON(!list_empty(&cc.freepages)); 2319 VM_BUG_ON(!list_empty(&cc.migratepages)); 2320 2321 *capture = capc.page; ^^^^^^^^ Unchecked dereference. 2322 current->capture_control = NULL; 2323 In practice this is not an issue, as the only caller path passes non-NULL capture: __alloc_pages_direct_compact() struct page *page = NULL; try_to_compact_pages(capture = &page); compact_zone_order(capture = capture); So let's remove the unnecessary check, which should also make Smatch happy. Link: http://lkml.kernel.org/r/18b0df3c-0589-d96c-23fa-040798fee187@suse.cz Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction") Reported-by: Dan Carpenter Suggested-by: Andrew Morton Signed-off-by: Vlastimil Babka Acked-by: Mel Gorman Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton --- mm/compaction.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/compaction.c~mm-compaction-fully-assume-capture-is-not-null-in-compact_zone_order +++ a/mm/compaction.c @@ -2314,8 +2314,7 @@ static enum compact_result compact_zone_ .page = NULL, }; - if (capture) - current->capture_control = &capc; + current->capture_control = &capc; ret = compact_zone(&cc, &capc); @@ -2337,6 +2336,7 @@ int sysctl_extfrag_threshold = 500; * @alloc_flags: The allocation flags of the current allocation * @ac: The context of current allocation * @prio: Determines how hard direct compaction should try to succeed + * @capture: Pointer to free page created by compaction will be stored here * * This is the main entry point for direct page compaction. */ _