On Sun, Feb 19, 2017 at 10:32:43AM +0100, Christian König wrote:
> Am 18.02.2017 um 23:50 schrieb Nicolai Hähnle:
> > From: Nicolai Hähnle <nicolai.haehnle at amd.com>
> >
> > The vm fault handler relies on the fact that the VMA owns a reference
> > to the BO. However, once mmap_sem is released, other tasks are free to
> > destroy the VMA, which can lead to the BO being freed. Fix two code
> > paths where that can happen, both related to vm fault retries.
> >
> > Found via a lock debugging warning which flagged &bo->wu_mutex as
> > locked while being destroyed.
> >
> > Fixes: cbe12e74ee4e ("drm/ttm: Allow vm fault retries")
> > Signed-off-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
>
> Good catch! Patch is Reviewed-by: Christian König <christian.koenig at amd.com>
Since you have commit rights and all, care to push to drm-misc.git?
-Daniel
>
> > --
> > This does not fix the random memory corruption I've been seeing.
> > ---
> > drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > index a6ed9d5..750733a 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > @@ -66,8 +66,11 @@ static int ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
> > if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
> > goto out_unlock;
> > + ttm_bo_reference(bo);
> > up_read(&vma->vm_mm->mmap_sem);
> > (void) fence_wait(bo->moving, true);
> > + ttm_bo_unreserve(bo);
> > + ttm_bo_unref(&bo);
> > goto out_unlock;
> > }
> > @@ -120,8 +123,10 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> > if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
> > if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
> > + ttm_bo_reference(bo);
> > up_read(&vma->vm_mm->mmap_sem);
> > (void) ttm_bo_wait_unreserved(bo);
> > + ttm_bo_unref(&bo);
> > }
> > return VM_FAULT_RETRY;
> > @@ -166,6 +171,13 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> > ret = ttm_bo_vm_fault_idle(bo, vma, vmf);
> > if (unlikely(ret != 0)) {
> > retval = ret;
> > +
> > + if (retval == VM_FAULT_RETRY &&
> > + !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
> > + /* The BO has already been unreserved. */
> > + return retval;
> > + }
> > +
> > goto out_unlock;
> > }
>
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
