Re: [PATCH RFC 1/5] vpda: try to fix the potential crash due to misusing __GFP_NOFAIL

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Thu, Jul 25, 2024 at 6:08 PM Michal Hocko <mhocko@xxxxxxxx> wrote:
>
> On Thu 25-07-24 10:50:45, Barry Song wrote:
> > On Thu, Jul 25, 2024 at 12:27 AM Michal Hocko <mhocko@xxxxxxxx> wrote:
> > >
> > > On Wed 24-07-24 20:55:40, Barry Song wrote:
> [...]
> > > > diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
> > > > index 791d38d6284c..eff700e5f7a2 100644
> > > > --- a/drivers/vdpa/vdpa_user/iova_domain.c
> > > > +++ b/drivers/vdpa/vdpa_user/iova_domain.c
> > > > @@ -287,28 +287,44 @@ void vduse_domain_remove_user_bounce_pages(struct vduse_iova_domain *domain)
> > > >  {
> > > >       struct vduse_bounce_map *map;
> > > >       unsigned long i, count;
> > > > +     struct page **pages = NULL;
> > > >
> > > >       write_lock(&domain->bounce_lock);
> > > >       if (!domain->user_bounce_pages)
> > > >               goto out;
> > > > -
> > > >       count = domain->bounce_size >> PAGE_SHIFT;
> > > > +     write_unlock(&domain->bounce_lock);
> > > > +
> > > > +     pages = kmalloc_array(count, sizeof(*pages), GFP_KERNEL | __GFP_NOFAIL);
> > > > +     for (i = 0; i < count; i++)
> > > > +             pages[i] = alloc_page(GFP_KERNEL | __GFP_NOFAIL);
> > >
> > > AFAICS vduse_domain_release calls this function with
> > > spin_lock(&domain->iotlb_lock) so dropping &domain->bounce_lock is not
> > > sufficient.
> >
> > yes. this is true:
> >
> > static int vduse_domain_release(struct inode *inode, struct file *file)
> > {
> >         struct vduse_iova_domain *domain = file->private_data;
> >
> >         spin_lock(&domain->iotlb_lock);
> >         vduse_iotlb_del_range(domain, 0, ULLONG_MAX);
> >         vduse_domain_remove_user_bounce_pages(domain);
> >         vduse_domain_free_kernel_bounce_pages(domain);
> >         spin_unlock(&domain->iotlb_lock);
> >         put_iova_domain(&domain->stream_iovad);
> >         put_iova_domain(&domain->consistent_iovad);
> >         vhost_iotlb_free(domain->iotlb);
> >         vfree(domain->bounce_maps);
> >         kfree(domain);
> >
> >         return 0;
> > }
> >
> > This is quite a pain. I admit I don't have knowledge of this driver, and I don't
> > think it's safe to release two locks and then reacquire them. The situation is
> > rather complex. Therefore, I would prefer if the VDPA maintainers could
> > take the lead in implementing a proper fix.
>
> Would it be possible to move all that work to a deferred context?

My understanding is that we need to be aware of both the iotlb_lock and
bounce_lock to implement the correct changes. As long as we still need
to acquire these two locks in a deferred context, there doesn't seem to
be any difference.

I can do the memory pre-allocation before spin_lock(&domain->iotlb_lock),
but I have no knowledge whether the "count" will change after I make
the preallocation.

diff --git a/drivers/vdpa/vdpa_user/iova_domain.c
b/drivers/vdpa/vdpa_user/iova_domain.c
index 791d38d6284c..7ec87ef33d42 100644
--- a/drivers/vdpa/vdpa_user/iova_domain.c
+++ b/drivers/vdpa/vdpa_user/iova_domain.c
@@ -544,9 +544,12 @@ static int vduse_domain_release(struct inode
*inode, struct file *file)
 {
        struct vduse_iova_domain *domain = file->private_data;

+      struct page **pages;
+      spin_lock(&domain->iotlb_lock); maybe also + bounce_lock?
+      count = domain->bounce_size >> PAGE_SHIFT;
+      spin_unlock(&domain->iotlb_lock);
+
+       preallocate_count_pages(pages, count);
+
....
        spin_lock(&domain->iotlb_lock);
        vduse_iotlb_del_range(domain, 0, ULLONG_MAX);
-       vduse_domain_remove_user_bounce_pages(domain);
+       vduse_domain_remove_user_bounce_pages(domain, pages);
        vduse_domain_free_kernel_bounce_pages(domain);
        spin_unlock(&domain->iotlb_lock);
        put_iova_domain(&domain->stream_iovad);


> --
> Michal Hocko
> SUSE Labs





[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux