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    SubjectRe: [PATCH 5/8] trace_uprobe: Support SDT markers having reference count (semaphore)
    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();

    Oleg.

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