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| author | Vlastimil Babka <vbabka@suse.cz> | 2020-04-01 21:10:35 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-04-02 09:35:31 -0700 |
| commit | 6467552ca64c4ddd2b83ed73192107d7145f533b (patch) | |
| tree | 6a82012f652237d6b3c35fef2b75a3f5f9283211 | |
| parent | 1da2f328fa643bd72197dfed0c655148af31e4eb (diff) | |
| download | unicode-6467552ca64c4ddd2b83ed73192107d7145f533b.tar.gz | |
mm, compaction: fully assume capture is not NULL in compact_zone_order()
Dan reports:
The patch 5e1f0f098b46: "mm, compaction: capture a page under direct
compaction" from Mar 5, 2019, leads to the following Smatch complaint:
mm/compaction.c:2321 compact_zone_order()
error: we previously assumed 'capture' could be null (see line 2313)
mm/compaction.c
2288 static enum compact_result compact_zone_order(struct zone *zone, int order,
2289 gfp_t gfp_mask, enum compact_priority prio,
2290 unsigned int alloc_flags, int classzone_idx,
2291 struct page **capture)
^^^^^^^
2313 if (capture)
^^^^^^^
Check for NULL
2314 current->capture_control = &capc;
2315
2316 ret = compact_zone(&cc, &capc);
2317
2318 VM_BUG_ON(!list_empty(&cc.freepages));
2319 VM_BUG_ON(!list_empty(&cc.migratepages));
2320
2321 *capture = capc.page;
^^^^^^^^
Unchecked dereference.
2322 current->capture_control = NULL;
2323
In practice this is not an issue, as the only caller path passes non-NULL
capture:
__alloc_pages_direct_compact()
struct page *page = NULL;
try_to_compact_pages(capture = &page);
compact_zone_order(capture = capture);
So let's remove the unnecessary check, which should also make Smatch happy.
Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: http://lkml.kernel.org/r/18b0df3c-0589-d96c-23fa-040798fee187@suse.cz
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/compaction.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/compaction.c b/mm/compaction.c index 000ade085b8919..07947387244a0d 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -2314,8 +2314,7 @@ static enum compact_result compact_zone_order(struct zone *zone, int order, .page = NULL, }; - if (capture) - current->capture_control = &capc; + current->capture_control = &capc; ret = compact_zone(&cc, &capc); @@ -2337,6 +2336,7 @@ int sysctl_extfrag_threshold = 500; * @alloc_flags: The allocation flags of the current allocation * @ac: The context of current allocation * @prio: Determines how hard direct compaction should try to succeed + * @capture: Pointer to free page created by compaction will be stored here * * This is the main entry point for direct page compaction. */ |