[ Upstream commit dd7ef7bd14640f11763b54f55131000165f48321 ] 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 [akpm@xxxxxxxxxxxxxxxxxxxx: code cleanup] Link: http://lkml.kernel.org/r/20190320203338.53367-1-cai@xxxxxx Fixes: 70b44595eafe ("mm, compaction: use free lists to quickly locate a migration source") Signed-off-by: Qian Cai <cai@xxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- mm/compaction.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/compaction.c b/mm/compaction.c index 368445cc71cf..2d7bb9eb07cd 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1164,7 +1164,9 @@ 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; + unsigned short shift = BITS_PER_LONG - 1; + + return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1; } /* -- 2.20.1
