Messages in this thread | | | Subject | Re: [RFC PATCH 1/1] mm/percpu.c: fix memory leakage issue when allocate a odd alignment area | From | zijun_hu <> | Date | Wed, 12 Oct 2016 15:24:33 +0800 |
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On 10/12/2016 02:53 PM, Michal Hocko wrote: > On Wed 12-10-16 08:28:17, zijun_hu wrote: >> On 2016/10/12 1:22, Michal Hocko wrote: >>> On Tue 11-10-16 21:24:50, zijun_hu wrote: >>>> From: zijun_hu <zijun_hu@htc.com> >>>> >>>> the LSB of a chunk->map element is used for free/in-use flag of a area >>>> and the other bits for offset, the sufficient and necessary condition of >>>> this usage is that both size and alignment of a area must be even numbers >>>> however, pcpu_alloc() doesn't force its @align parameter a even number >>>> explicitly, so a odd @align maybe causes a series of errors, see below >>>> example for concrete descriptions. >>> >>> Is or was there any user who would use a different than even (or power of 2) >>> alighment? If not is this really worth handling? >>> >> >> it seems only a power of 2 alignment except 1 can make sure it work very well, >> that is a strict limit, maybe this more strict limit should be checked > > I fail to see how any other alignment would actually make any sense > what so ever. Look, I am not a maintainer of this code but adding a new > code to catch something that doesn't make any sense sounds dubious at > best to me. > > I could understand this patch if you see a problem and want to prevent > it from repeating bug doing these kind of changes just in case sounds > like a bad idea. >
thanks for your reply
should we have a generic discussion whether such patches which considers many boundary or rare conditions are necessary.
i found the following code segments in mm/vmalloc.c static struct vmap_area *alloc_vmap_area(unsigned long size, unsigned long align, unsigned long vstart, unsigned long vend, int node, gfp_t gfp_mask) { ...
BUG_ON(!size); BUG_ON(offset_in_page(size)); BUG_ON(!is_power_of_2(align));
should we make below declarations as conventions 1) when we say 'alignment', it means align to a power of 2 value for example, aligning value @v to @b implicit @v is power of 2 , align 10 to 4 is 12 2) when we say 'round value @v up/down to boundary @b', it means the result is a times of @b, it don't requires @b is a power of 2
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