drm/amdkfd: unbind only existing processes

When unbinding a process from a device (initiated by amd_iommu_v2), the
driver needs to make sure that process still exists in the process table.
There is a possibility that amdkfd's own notifier handler -
kfd_process_notifier_release() - was called before the unbind function
and it already removed the process from the process table.

v2:
Because there can be only one process with the specified pasid, and
because *p can't be NULL inside the hash_for_each_rcu macro, it is more
reasonable to just put the whole code inside the if statement that
compares the pasid value. That way, when we exit hash_for_each_rcu, we
simply exit the function as well.

Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
CC: Stable <stable@vger.kernel.org>

1 files changed, 35 insertions, 25 deletions

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
index ac005796b71c..a64bc619ed82 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
@@ -404,42 +404,52 @@ void kfd_unbind_process_from_device(struct kfd_dev *dev, unsigned int pasid)
 
         idx = srcu_read_lock(&kfd_processes_srcu);
 
+        /*
+         * Look for the process that matches the pasid. If there is no such
+         * process, we either released it in amdkfd's own notifier, or there
+         * is a bug. Unfortunately, there is no way to tell...
+         */
         hash_for_each_rcu(kfd_processes_table, i, p, kfd_processes)
-                if (p->pasid == pasid)
-                        break;
+                if (p->pasid == pasid) {
 
-        srcu_read_unlock(&kfd_processes_srcu, idx);
+                        srcu_read_unlock(&kfd_processes_srcu, idx);
 
-        BUG_ON(p->pasid != pasid);
+                        pr_debug("Unbinding process %d from IOMMU\n", pasid);
 
-        mutex_lock(&p->mutex);
+                        mutex_lock(&p->mutex);
 
-        if ((dev->dbgmgr) && (dev->dbgmgr->pasid == p->pasid))
-                kfd_dbgmgr_destroy(dev->dbgmgr);
+                        if ((dev->dbgmgr) && (dev->dbgmgr->pasid == p->pasid))
+                                kfd_dbgmgr_destroy(dev->dbgmgr);
 
-        pqm_uninit(&p->pqm);
+                        pqm_uninit(&p->pqm);
 
-        pdd = kfd_get_process_device_data(dev, p);
+                        pdd = kfd_get_process_device_data(dev, p);
 
-        if (!pdd) {
-                mutex_unlock(&p->mutex);
-                return;
-        }
+                        if (!pdd) {
+                                mutex_unlock(&p->mutex);
+                                return;
+                        }
 
-        if (pdd->reset_wavefronts) {
-                dbgdev_wave_reset_wavefronts(pdd->dev, p);
-                pdd->reset_wavefronts = false;
-        }
+                        if (pdd->reset_wavefronts) {
+                                dbgdev_wave_reset_wavefronts(pdd->dev, p);
+                                pdd->reset_wavefronts = false;
+                        }
 
-        /*
-         * Just mark pdd as unbound, because we still need it to call
-         * amd_iommu_unbind_pasid() in when the process exits.
-         * We don't call amd_iommu_unbind_pasid() here
-         * because the IOMMU called us.
-         */
-        pdd->bound = false;
+                        /*
+                         * Just mark pdd as unbound, because we still need it
+                         * to call amd_iommu_unbind_pasid() in when the
+                         * process exits.
+                         * We don't call amd_iommu_unbind_pasid() here
+                         * because the IOMMU called us.
+                         */
+                        pdd->bound = false;
 
-        mutex_unlock(&p->mutex);
+                        mutex_unlock(&p->mutex);
+
+                        return;
+                }
+
+        srcu_read_unlock(&kfd_processes_srcu, idx);
 }
 
 struct kfd_process_device *kfd_get_first_process_device_data(struct kfd_process *p)