nouveau: unlock mmap_sem on all errors from nouveau_range_fault

Currently nouveau_svm_fault expects nouveau_range_fault to never unlock
mmap_sem, but the latter unlocks it for a random selection of error
codes. Fix this up by always unlocking mmap_sem for non-zero return values
in nouveau_range_fault, and only unlocking it in the caller for successful
returns.

Link: https://lore.kernel.org/r/20190724065258.16603-5-hch@lst.de
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index e309749..a835ceb 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -495,8 +495,10 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct hmm_range *range)
        ret = hmm_range_register(range, mirror,
                                 range->start, range->end,
                                 PAGE_SHIFT);
-       if (ret)
+       if (ret) {
+               up_read(&range->vma->vm_mm->mmap_sem);
                return (int)ret;
+       }
 
        if (!hmm_range_wait_until_valid(range, HMM_RANGE_DEFAULT_TIMEOUT)) {
                up_read(&range->vma->vm_mm->mmap_sem);
@@ -505,10 +507,9 @@ nouveau_range_fault(struct hmm_mirror *mirror, struct hmm_range *range)
 
        ret = hmm_range_fault(range, true);
        if (ret <= 0) {
-               if (ret == -EBUSY || !ret) {
-                       up_read(&range->vma->vm_mm->mmap_sem);
+               if (ret == 0)
                        ret = -EBUSY;
-               }
+               up_read(&range->vma->vm_mm->mmap_sem);
                hmm_range_unregister(range);
                return ret;
        }
@@ -706,8 +707,8 @@ again:
                                                NULL);
                        svmm->vmm->vmm.object.client->super = false;
                        mutex_unlock(&svmm->mutex);
+                       up_read(&svmm->mm->mmap_sem);
                }
-               up_read(&svmm->mm->mmap_sem);
 
                /* Cancel any faults in the window whose pages didn't manage
                 * to keep their valid bit, or stay writeable when required.