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[195.135.220.15]) by mx.google.com with ESMTPS id g6si1618073edm.219.2019.03.14.01.25.28 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 14 Mar 2019 01:25:28 -0700 (PDT) Received-SPF: pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=pass (google.com: domain of vbabka@suse.cz designates 195.135.220.15 as permitted sender) smtp.mailfrom=vbabka@suse.cz X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 36A06ACE3; Thu, 14 Mar 2019 08:25:28 +0000 (UTC) Subject: Re: [RESEND PATCH] mm/compaction: fix an undefined behaviour To: Qian Cai , akpm@linux-foundation.org Cc: mgorman@techsingularity.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190313180616.47908-1-cai@lca.pw> From: Vlastimil Babka Message-ID: <433eedda-bba6-798d-31e8-d603fa33a20d@suse.cz> Date: Thu, 14 Mar 2019 09:25:27 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.2 MIME-Version: 1.0 In-Reply-To: <20190313180616.47908-1-cai@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 3/13/19 7:06 PM, Qian Cai wrote: > In a low-memory situation, cc->fast_search_fail can keep increasing as > it is unable to find an available page to isolate in > fast_isolate_freepages(). As the result, it could trigger an error > below, so just compare with the maximum bits can be shifted first. > > UBSAN: Undefined behaviour in mm/compaction.c:1160:30 > shift exponent 64 is too large for 64-bit type 'unsigned long' > CPU: 131 PID: 1308 Comm: kcompactd1 Kdump: loaded Tainted: G > W L 5.0.0+ #17 > Call trace: > dump_backtrace+0x0/0x450 > show_stack+0x20/0x2c > dump_stack+0xc8/0x14c > __ubsan_handle_shift_out_of_bounds+0x7e8/0x8c4 > compaction_alloc+0x2344/0x2484 > unmap_and_move+0xdc/0x1dbc > migrate_pages+0x274/0x1310 > compact_zone+0x26ec/0x43bc > kcompactd+0x15b8/0x1a24 > kthread+0x374/0x390 > ret_from_fork+0x10/0x18 > > Fixes: 70b44595eafe ("mm, compaction: use free lists to quickly locate a migration source") > Acked-by: Mel Gorman > Signed-off-by: Qian Cai Acked-by: Vlastimil Babka > --- > > Resend because Andrew's email was bounced back at some point. > > mm/compaction.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index f171a83707ce..6aebf1eb8d98 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1157,7 +1157,9 @@ static bool suitable_migration_target(struct compact_control *cc, > static inline unsigned int > freelist_scan_limit(struct compact_control *cc) > { > - return (COMPACT_CLUSTER_MAX >> cc->fast_search_fail) + 1; > + return (COMPACT_CLUSTER_MAX >> > + min((unsigned short)(BITS_PER_LONG - 1), cc->fast_search_fail)) > + + 1; > } > > /* >