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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id s49sm5429876qtk.7.2019.03.08.14.47.03 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Mar 2019 14:47:03 -0800 (PST) From: Qian Cai To: akpm@linux-foundation.org Cc: mgorman@techsingularity.net, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qian Cai Subject: [PATCH] mm/compaction: fix an undefined behaviour Date: Fri, 8 Mar 2019 17:46:50 -0500 Message-Id: <20190308224650.68955-1-cai@lca.pw> X-Mailer: git-send-email 2.17.2 (Apple Git-113) 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: X-Virus-Scanned: ClamAV using ClamSMTP 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") Signed-off-by: Qian Cai Acked-by: Mel Gorman --- 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; } /*