Re: [PATCH 12/33] userfaultfd: non-cooperative: Add madvise() event for MADV_DONTNEED request

[Mike Rapoport <rppt@linux.vnet.ibm.com>]

On Thu, Nov 03, 2016 at 04:01:12PM +0800, Hillf Danton wrote:
> On Thursday, November 03, 2016 3:34 AM Andrea Arcangeli wrote:
> > +void madvise_userfault_dontneed(struct vm_area_struct *vma,
> > +				struct vm_area_struct **prev,
> > +				unsigned long start, unsigned long end)
> > +{
> > +	struct userfaultfd_ctx *ctx;
> > +	struct userfaultfd_wait_queue ewq;
> > +
> > +	ctx = vma->vm_userfaultfd_ctx.ctx;
> > +	if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_MADVDONTNEED))
> > +		return;
> > +
> > +	userfaultfd_ctx_get(ctx);
> > +	*prev = NULL; /* We wait for ACK w/o the mmap semaphore */
> > +	up_read(&vma->vm_mm->mmap_sem);
> > +
> > +	msg_init(&ewq.msg);
> > +
> > +	ewq.msg.event = UFFD_EVENT_MADVDONTNEED;
> > +	ewq.msg.arg.madv_dn.start = start;
> > +	ewq.msg.arg.madv_dn.end = end;
> > +
> > +	userfaultfd_event_wait_completion(ctx, &ewq);
> > +
> > +	down_read(&vma->vm_mm->mmap_sem);
> 
> After napping with mmap_sem released, is vma still valid?
> 
> > +}
> > +

Below is the updated patch that accesses mmap_sem via local reference to
mm_struct rather than via vma.