On Mon, 2014-01-27 at 16:02 -0500, Naoya Horiguchi wrote:
> On Sun, Jan 26, 2014 at 07:52:21PM -0800, Davidlohr Bueso wrote:
> > From: Joonsoo Kim <iamjoonsoo....@lge.com>
> >
> > There is a race condition if we map a same file on different processes.
> > Region tracking is protected by mmap_sem and hugetlb_instantiation_mutex.
> > When we do mmap, we don't grab a hugetlb_instantiation_mutex, but only the,
> > mmap_sem (exclusively). This doesn't prevent other tasks from modifying the
> > region structure, so it can be modified by two processes concurrently.
> >
> > To solve this, introduce a spinlock to resv_map and make region manipulation
> > function grab it before they do actual work.
> >
> > Acked-by: David Gibson <da...@gibson.dropbear.id.au>
> > Signed-off-by: Joonsoo Kim <iamjoonsoo....@lge.com>
> > [Updated changelog]
> > Signed-off-by: Davidlohr Bueso <davidl...@hp.com>
> > ---
> ...
> > @@ -203,15 +200,23 @@ static long region_chg(struct resv_map *resv, long f,
> > long t)
> > * Subtle, allocate a new region at the position but make it zero
> > * size such that we can guarantee to record the reservation. */
> > if (&rg->link == head || t < rg->from) {
> > - nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
> > - if (!nrg)
> > - return -ENOMEM;
> > + if (!nrg) {
> > + spin_unlock(&resv->lock);
>
> I think that doing kmalloc() inside the lock is simpler.
> Why do you unlock and retry here?
This is a spinlock, no can do -- we've previously debated this and since
the critical region is quite small, a non blocking lock is better suited
here. We do the retry so we don't race once the new region is allocated
after the lock is dropped.
Thanks,
Davidlohr
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