Re: [PATCH 3/7] revoke: core code

From: Peter Zijlstra
Date: Fri Mar 09 2007 - 18:12:51 EST


On Fri, 2007-03-09 at 10:15 +0200, Pekka J Enberg wrote:

> +static int revoke_vma(struct vm_area_struct *vma, struct zap_details *details)
> +{
> + unsigned long restart_addr, start_addr, end_addr;
> + int need_break;
> +
> + start_addr = vma->vm_start;
> + end_addr = vma->vm_end;
> +
> + /*
> + * Not holding ->mmap_sem here.
> + */
> + vma->vm_flags |= VM_REVOKED;
> + smp_mb();

Hmm, i_mmap_lock pins the vma and excludes modifications, but doesn't
exclude concurrent faults.

I guess its save.

> + again:
> + restart_addr = zap_page_range(vma, start_addr, end_addr - start_addr,
> + details);
> +
> + need_break = need_resched() || need_lockbreak(details->i_mmap_lock);
> + if (need_break)
> + goto out_need_break;
> +
> + if (restart_addr < end_addr) {
> + start_addr = restart_addr;
> + goto again;
> + }
> + return 0;
> +
> + out_need_break:
> + spin_unlock(details->i_mmap_lock);
> + cond_resched();
> + spin_lock(details->i_mmap_lock);
> + return -EINTR;

I'm not sure this scheme works, given a sufficiently loaded machine,
this might never complete.

> +}
> +
> +static int revoke_mapping(struct address_space *mapping, struct file *to_exclude)
> +{
> + struct vm_area_struct *vma;
> + struct prio_tree_iter iter;
> + struct zap_details details;
> + int err = 0;
> +
> + details.i_mmap_lock = &mapping->i_mmap_lock;
> +
> + spin_lock(&mapping->i_mmap_lock);
> + vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, ULONG_MAX) {
> + if (vma->vm_flags & VM_SHARED && vma->vm_file != to_exclude) {

I'm never sure of operator precedence and prefer:

(vma->vm_flags & VM_SHARED) && ...

which leaves no room for error.

> + err = revoke_vma(vma, &details);
> + if (err)
> + goto out;
> + }
> + }
> +
> + list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) {
> + if (vma->vm_flags & VM_SHARED && vma->vm_file != to_exclude) {

Idem.

> + err = revoke_vma(vma, &details);
> + if (err)
> + goto out;
> + }
> + }
> + out:
> + spin_unlock(&mapping->i_mmap_lock);
> + return err;
> +}


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