On 7/14/20 3:02 AM, Vlastimil Babka wrote: > On 7/14/20 11:57 AM, Wei Yang wrote: >> On Tue, Jul 14, 2020 at 11:22:03AM +0200, Vlastimil Babka wrote: >>> On 7/14/20 11:13 AM, Vlastimil Babka wrote: >>>> On 7/14/20 9:34 AM, Wei Yang wrote: >>>>> The second parameter of for_each_node_mask_to_[alloc|free] is a loop >>>>> variant, which is not used outside of loop iteration. >>>>> >>>>> Let's hide this. >>>>> >>>>> Signed-off-by: Wei Yang <richard.weiy...@linux.alibaba.com> >>>>> --- >>>>> mm/hugetlb.c | 38 ++++++++++++++++++++------------------ >>>>> 1 file changed, 20 insertions(+), 18 deletions(-) >>>>> >>>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>>>> index 57ece74e3aae..9c3d15fb317e 100644 >>>>> --- a/mm/hugetlb.c >>>>> +++ b/mm/hugetlb.c >>>>> @@ -1196,17 +1196,19 @@ static int hstate_next_node_to_free(struct hstate >>>>> *h, nodemask_t *nodes_allowed) >>>>> return nid; >>>>> } >>>>> >>>>> -#define for_each_node_mask_to_alloc(hs, nr_nodes, node, mask) >>>>> \ >>>>> - for (nr_nodes = nodes_weight(*mask); \ >>>>> - nr_nodes > 0 && \ >>>>> +#define for_each_node_mask_to_alloc(hs, node, mask) >>>>> \ >>>>> + int __nr_nodes; \ >>>>> + for (__nr_nodes = nodes_weight(*mask); \ >>>> >>>> The problem with this is that if I use the macro twice in the same block, >>>> this >>>> will redefine __nr_nodes and fail to compile, no? >>>> In that case it's better to avoid setting up this trap, IMHO. >>> >>> Ah, and it will also generate the following warning, if the use of for_each* >>> macro is not the first thing after variable declarations, but there's >>> another >>> statement before: >>> >>> warning: ISO C90 forbids mixed declarations and code >>> [-Wdeclaration-after-statement] >>> >>> Instead we should switch to C99 and declare it as "for (int __nr_nodes" :P >> >> Hmm... I tried what you suggested, but compiler complains. >> >> 'for' loop initial declarations are only allowed in C99 or C11 mode > > Yes, by "we should switch to C99" I meant that the kernel kbuild system would > need to switch. Not a trivial change... > Without that, I don't see how your patch is possible to do safely.
Vlastimil, thanks for pointing out future potential issues with this patch. I likely would have missed that. Wei, thanks for taking the time to put together the patch. However, I tend to agree with Vlastimil's assesment. The cleanup is not worth the risk of running into issues if someone uses multiple instances of the macro. -- Mike Kravetz
