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SubjectRe: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore)
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On 03/15/2018 08:31 PM, Oleg Nesterov wrote:
> On 03/13, Ravi Bangoria wrote:
>> +sdt_update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
>> +{
>> + void *kaddr;
>> + struct page *page;
>> + struct vm_area_struct *vma;
>> + int ret = 0;
>> + unsigned short orig = 0;
>> +
>> + if (vaddr == 0)
>> + return -EINVAL;
>> +
>> + ret = get_user_pages_remote(NULL, mm, vaddr, 1,
>> + FOLL_FORCE | FOLL_WRITE, &page, &vma, NULL);
>> + if (ret <= 0)
>> + return ret;
>> +
>> + kaddr = kmap_atomic(page);
>> + memcpy(&orig, kaddr + (vaddr & ~PAGE_MASK), sizeof(orig));
>> + orig += d;
>> + memcpy(kaddr + (vaddr & ~PAGE_MASK), &orig, sizeof(orig));
>> + kunmap_atomic(kaddr);
> Hmm. Why memcpy? You could simply do
>
> kaddr = kmap_atomic();
> unsigned short *ptr = kaddr + (vaddr & ~PAGE_MASK);
> *ptr += d;
> kunmap_atomic();

Yes, that should work. Will change it.

Thanks for the review,
Ravi

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