On Fri, 29 Nov 2019 14:24:48 +0000
Steven Price <steven.price@xxxxxxx> wrote:
> On 29/11/2019 13:59, Boris Brezillon wrote:
> > If 2 threads change the MADVISE property of the same BO in parallel we
> > might end up with an shmem->madv value that's inconsistent with the
> > presence of the BO in the shrinker list.
>
> I'm a bit worried from the point of view of user space sanity that you
> observed this - but clearly the kernel should be robust!
It's not something I observed, just found the race by inspecting the
code, and I thought it was worth fixing it.
>
> >
> > The easiest solution to fix that is to protect the
> > drm_gem_shmem_madvise() call with the shrinker lock.
> >
> > Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
>
> Reviewed-by: Steven Price <steven.price@xxxxxxx>
Thanks.
>
> > ---
> > drivers/gpu/drm/panfrost/panfrost_drv.c | 9 ++++-----
> > 1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > index f21bc8a7ee3a..efc0a24d1f4c 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > @@ -347,20 +347,19 @@ static int panfrost_ioctl_madvise(struct drm_device *dev, void *data,
> > return -ENOENT;
> > }
> >
> > + mutex_lock(&pfdev->shrinker_lock);
> > args->retained = drm_gem_shmem_madvise(gem_obj, args->madv);
> >
> > if (args->retained) {
> > struct panfrost_gem_object *bo = to_panfrost_bo(gem_obj);
> >
> > - mutex_lock(&pfdev->shrinker_lock);
> > -
> > if (args->madv == PANFROST_MADV_DONTNEED)
> > - list_add_tail(&bo->base.madv_list, &pfdev->shrinker_list);
> > + list_add_tail(&bo->base.madv_list,
> > + &pfdev->shrinker_list);
> > else if (args->madv == PANFROST_MADV_WILLNEED)
> > list_del_init(&bo->base.madv_list);
> > -
> > - mutex_unlock(&pfdev->shrinker_lock);
> > }
> > + mutex_unlock(&pfdev->shrinker_lock);
> >
> > drm_gem_object_put_unlocked(gem_obj);
> > return 0;
> >
>
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