Re: [PATCH v2] RDMA/umem: minor bug fix and cleanup in error handling paths

Artemy Kovalyov
2019-03-03T09:52:41Z

On 02/03/2019 21:44, Ira Weiny wrote:
>
> On Sat, Mar 02, 2019 at 12:24:35PM -0800, john.hubbard@gmail.com wrote:
>> From: John Hubbard <jhubbard@nvidia.com>
>>
>> ...
>> 3. Dead code removal: the check for (user_virt & ~page_mask)
>> is checking for a condition that can never happen,
>> because earlier:
>>
>> user_virt = user_virt & page_mask;
>>
>> ...so, remove that entire phrase.
>>
>>
>> bcnt -= min_t(size_t, npages << PAGE_SHIFT, bcnt);
>> mutex_lock(&umem_odp->umem_mutex);
>> for (j = 0; j < npages; j++, user_virt += PAGE_SIZE) {
>> - if (user_virt & ~page_mask) {
>> - p += PAGE_SIZE;
>> - if (page_to_phys(local_page_list[j]) != p) {
>> - ret = -EFAULT;
>> - break;
>> - }
>> - put_page(local_page_list[j]);
>> - continue;
>> - }
>> -
>
> I think this is trying to account for compound pages. (ie page_mask could
> represent more than PAGE_SIZE which is what user_virt is being incrimented by.)
> But putting the page in that case seems to be the wrong thing to do?
>
> Yes this was added by Artemy[1] now cc'ed.

Right, this is for huge pages, please keep it.
put_page() needed to decrement refcount of the head page.