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authorVlastimil Babka <vbabka@suse.cz>2020-04-02 07:10:35 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-07-09 10:37:57 +0300
commit64a94c550c4440dc9d61d681145382f92968266c (patch)
tree509c1efa3894d43eec4f31cb9632fce29f353e82 /mm
parent2a9278ac9c5515b372fbc831d7b0702096dc3127 (diff)
downloadlinux-64a94c550c4440dc9d61d681145382f92968266c.tar.xz
mm, compaction: fully assume capture is not NULL in compact_zone_order()
commit 6467552ca64c4ddd2b83ed73192107d7145f533b upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/compaction.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/compaction.c b/mm/compaction.c
index 672d3c78c6ab..35c991fbf983 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2310,8 +2310,7 @@ 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);
@@ -2333,6 +2332,7 @@ 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.
*/