From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: + mm-compaction-fully-assume-capture-is-not-null-in-compact_zone_order.patch added to -mm tree Date: Sat, 29 Feb 2020 20:42:26 -0800 Message-ID: <20200301044226.4SpLX7fJO%akpm@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:48848 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726063AbgCAEm1 (ORCPT ); Sat, 29 Feb 2020 23:42:27 -0500 Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, dan.carpenter@oracle.com, mgorman@techsingularity.net, mm-commits@vger.kernel.org, vbabka@suse.cz The patch titled Subject: mm, compaction: fully assume capture is not NULL in compact_zone_order() has been added to the -mm tree. Its filename is mm-compaction-fully-assume-capture-is-not-null-in-compact_zone_order.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-fully-assume-capture-is-not-null-in-compact_zone_order.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-fully-assume-capture-is-not-null-in-compact_zone_order.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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. */ _ Patches currently in -mm which might be from vbabka@suse.cz are mm-hotplug-fix-page-online-with-debug_pagealloc-compiled-but-not-enabled.patch mm-compaction-fully-assume-capture-is-not-null-in-compact_zone_order.patch