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!
>
> 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>
> ---
> 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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