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    SubjectRe: [PATCH v5 3.1.0-rc4-tip 18/26] uprobes: slot allocation.
    * Peter Zijlstra <peterz@infradead.org> [2011-09-27 13:49:37]:

    > On Tue, 2011-09-20 at 17:33 +0530, Srikar Dronamraju wrote:
    > > +static int xol_add_vma(struct uprobes_xol_area *area)
    > > +{
    > > + const struct cred *curr_cred;
    > > + struct vm_area_struct *vma;
    > > + struct mm_struct *mm;
    > > + unsigned long addr;
    > > + int ret = -ENOMEM;
    > > +
    > > + mm = get_task_mm(current);
    > > + if (!mm)
    > > + return -ESRCH;
    > > +
    > > + down_write(&mm->mmap_sem);
    > > + if (mm->uprobes_xol_area) {
    > > + ret = -EALREADY;
    > > + goto fail;
    > > + }
    > > +
    > > + /*
    > > + * Find the end of the top mapping and skip a page.
    > > + * If there is no space for PAGE_SIZE above
    > > + * that, mmap will ignore our address hint.
    > > + *
    > > + * override credentials otherwise anonymous memory might
    > > + * not be granted execute permission when the selinux
    > > + * security hooks have their way.
    > > + */
    > > + vma = rb_entry(rb_last(&mm->mm_rb), struct vm_area_struct, vm_rb);
    > > + addr = vma->vm_end + PAGE_SIZE;
    > > + curr_cred = override_creds(&init_cred);
    > > + addr = do_mmap_pgoff(NULL, addr, PAGE_SIZE, PROT_EXEC, MAP_PRIVATE, 0);
    > > + revert_creds(curr_cred);
    > > +
    > > + if (addr & ~PAGE_MASK)
    > > + goto fail;
    > > + vma = find_vma(mm, addr);
    > > +
    > > + /* Don't expand vma on mremap(). */
    > > + vma->vm_flags |= VM_DONTEXPAND | VM_DONTCOPY;
    > > + area->vaddr = vma->vm_start;
    > > + if (get_user_pages(current, mm, area->vaddr, 1, 1, 1, &area->page,
    > > + &vma) > 0)
    > > + ret = 0;
    > > +
    > > +fail:
    > > + up_write(&mm->mmap_sem);
    > > + mmput(mm);
    > > + return ret;
    > > +}
    >
    > So is that the right way? I looked back to the previous discussion with
    > Eric and couldn't really make up my mind either way. The changelog is
    > entirely without detail and Eric isn't CC'ed.

    This is based on what Stephen Smalley suggested on the same thread
    https://lkml.org/lkml/2011/4/20/224

    I used to keep the changelog after the marker after Christoph Hellwig
    had suggested that https://lkml.org/lkml/2010/7/20/5
    However "stg export" removes lines after the --- marker.

    I agree that I should have copied Eric and Stephen atleast on this
    patch. However if the number of to/cc are greater than 20, the LKML
    archive cool ignore the mail.

    I know that these arent problems faced by others and open to suggestions
    on how they have overcome the same.

    >
    > What's the point of having these discussions if all traces of them
    > disappear on the next posting?

    --
    Thanks and Regards
    Srikar



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