lkml.org 
[lkml]   [2019]   [Mar]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] mm/compaction: fix an undefined behaviour
Date
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)
\
 
 \ /
  Last update: 2019-03-08 23:47    [W:0.099 / U:0.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site