* [PATCH] mm/compaction: fix an undefined behaviour
@ 2019-03-08 22:46 Qian Cai
2019-03-09 0:28 ` Mel Gorman
0 siblings, 1 reply; 2+ messages in thread
From: Qian Cai @ 2019-03-08 22:46 UTC (permalink / raw)
To: akpm; +Cc: mgorman, vbabka, linux-mm, linux-kernel, Qian Cai
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 <cai@lca.pw>
---
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;
}
/*
--
2.17.2 (Apple Git-113)
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] mm/compaction: fix an undefined behaviour
2019-03-08 22:46 [PATCH] mm/compaction: fix an undefined behaviour Qian Cai
@ 2019-03-09 0:28 ` Mel Gorman
0 siblings, 0 replies; 2+ messages in thread
From: Mel Gorman @ 2019-03-09 0:28 UTC (permalink / raw)
To: Qian Cai; +Cc: akpm, vbabka, linux-mm, linux-kernel
On Fri, Mar 08, 2019 at 05:46:50PM -0500, 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")
> Signed-off-by: Qian Cai <cai@lca.pw>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
FWIW, I had seen the same message when trying to isolate potential
corruption (still unsuccessful, the tests always complete) but
considered it relatively benign and harmless. Still worth fixing so
thanks.
--
Mel Gorman
SUSE Labs
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