diff options
| author | Rasmus Villemoes <linux@rasmusvillemoes.dk> | 2017-07-10 15:49:26 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-07-10 16:32:32 -0700 |
| commit | b002529d256307602c669d1886c0b953b52b8700 (patch) | |
| tree | 9219954404a5b6124356dd8a1785d6f5c0653126 | |
| parent | 8c03cc85a035ae7a208c28c4382ecfeb6adf79a6 (diff) | |
mm/page_alloc.c: eliminate unsigned confusion in __rmqueue_fallback
Since current_order starts as MAX_ORDER-1 and is then only decremented,
the second half of the loop condition seems superfluous. However, if
order is 0, we may decrement current_order past 0, making it UINT_MAX.
This is obviously too subtle ([1], [2]).
Since we need to add some comment anyway, change the two variables to
signed, making the counting-down for loop look more familiar, and
apparently also making gcc generate slightly smaller code.
[1] https://lkml.org/lkml/2016/6/20/493
[2] https://lkml.org/lkml/2017/6/19/345
[akpm@linux-foundation.org: fix up reject fixupping]
Link: http://lkml.kernel.org/r/20170621185529.2265-1-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reported-by: Hao Lee <haolee.swjtu@gmail.com>
Acked-by: Wei Yang <weiyang@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/page_alloc.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 869035717048..d90c31951b90 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2206,12 +2206,16 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac, * list of requested migratetype, possibly along with other pages from the same * block, depending on fragmentation avoidance heuristics. Returns true if * fallback was found so that __rmqueue_smallest() can grab it. + * + * The use of signed ints for order and current_order is a deliberate + * deviation from the rest of this file, to make the for loop + * condition simpler. */ static inline bool -__rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) +__rmqueue_fallback(struct zone *zone, int order, int start_migratetype) { struct free_area *area; - unsigned int current_order; + int current_order; struct page *page; int fallback_mt; bool can_steal; @@ -2221,8 +2225,7 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) * approximates finding the pageblock with the most free pages, which * would be too costly to do exactly. */ - for (current_order = MAX_ORDER-1; - current_order >= order && current_order <= MAX_ORDER-1; + for (current_order = MAX_ORDER - 1; current_order >= order; --current_order) { area = &(zone->free_area[current_order]); fallback_mt = find_suitable_fallback(area, current_order, |