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    SubjectRe: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page replacement.
    * Stephen Wilson <wilsons@start.ca> [2011-03-14 12:58:18]:

    > On Mon, Mar 14, 2011 at 07:04:33PM +0530, Srikar Dronamraju wrote:
    > > +/**
    > > + * read_opcode - read the opcode at a given virtual address.
    > > + * @tsk: the probed task.
    > > + * @vaddr: the virtual address to store the opcode.
    > > + * @opcode: location to store the read opcode.
    > > + *
    > > + * For task @tsk, read the opcode at @vaddr and store it in @opcode.
    > > + * Return 0 (success) or a negative errno.
    > > + */
    > > +int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr,
    > > + uprobe_opcode_t *opcode)
    > > +{
    > > + struct vm_area_struct *vma;
    > > + struct page *page;
    > > + void *vaddr_new;
    > > + int ret;
    > > +
    > > + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma);
    > > + if (ret <= 0)
    > > + return -EFAULT;
    > > + ret = -EFAULT;
    > > +
    > > + /*
    > > + * check if the page we are interested is read-only mapped
    > > + * Since we are interested in text pages, Our pages of interest
    > > + * should be mapped read-only.
    > > + */
    > > + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) ==
    > > + (VM_READ|VM_EXEC))
    > > + goto put_out;
    > > +
    > > + lock_page(page);
    > > + vaddr_new = kmap_atomic(page, KM_USER0);
    > > + vaddr &= ~PAGE_MASK;
    > > + memcpy(&opcode, vaddr_new + vaddr, uprobe_opcode_sz);
    > > + kunmap_atomic(vaddr_new, KM_USER0);
    > > + unlock_page(page);
    > > + ret = uprobe_opcode_sz;
    >
    > This looks wrong. We should be setting ret = 0 on success here?

    Right, I should have set ret = 0 here.

    >
    > > +
    > > +put_out:
    > > + put_page(page); /* we did a get_page in the beginning */
    > > + return ret;
    > > +}
    >
    > --
    > steve
    >


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