[PATCH 1/2] drm/amdkfd: Use mmu_notifier_get

[Felix Kuehling]

We use mmu_notifier_put to free the MMU notifier. That needs to be
paired with mmu_notifier_get to work correctly. Othewrise the next patch
would cause a kernel oops.

Signed-off-by: Felix Kuehling <felix.kuehl...@amd.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_process.c | 33 +++++++++++++++++++-----
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c 
b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
index 2807e1c4d59b..145cd0a17d50 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
@@ -1011,6 +1011,16 @@ static void kfd_process_ref_release(struct kref *ref)
        queue_work(kfd_process_wq, &p->release_work);
 }
 
+static struct mmu_notifier *kfd_process_alloc_notifier(struct mm_struct *mm)
+{
+       int idx = srcu_read_lock(&kfd_processes_srcu);
+       struct kfd_process *p = find_process_by_mm(mm);
+
+       srcu_read_unlock(&kfd_processes_srcu, idx);
+
+       return p ? &p->mmu_notifier : ERR_PTR(-ESRCH);
+}
+
 static void kfd_process_free_notifier(struct mmu_notifier *mn)
 {
        kfd_unref_process(container_of(mn, struct kfd_process, mmu_notifier));
@@ -1075,6 +1085,7 @@ static void kfd_process_notifier_release(struct 
mmu_notifier *mn,
 
 static const struct mmu_notifier_ops kfd_process_mmu_notifier_ops = {
        .release = kfd_process_notifier_release,
+       .alloc_notifier = kfd_process_alloc_notifier,
        .free_notifier = kfd_process_free_notifier,
 };
 
@@ -1152,6 +1163,7 @@ static int kfd_process_device_init_cwsr_dgpu(struct 
kfd_process_device *pdd)
 static struct kfd_process *create_process(const struct task_struct *thread)
 {
        struct kfd_process *process;
+       struct mmu_notifier *mn;
        int err = -ENOMEM;
 
        process = kzalloc(sizeof(*process), GFP_KERNEL);
@@ -1182,19 +1194,28 @@ static struct kfd_process *create_process(const struct 
task_struct *thread)
        if (err != 0)
                goto err_init_apertures;
 
-       /* Must be last, have to use release destruction after this */
-       process->mmu_notifier.ops = &kfd_process_mmu_notifier_ops;
-       err = mmu_notifier_register(&process->mmu_notifier, process->mm);
-       if (err)
+       /* alloc_notifier needs to find the process in the hash table */
+       hash_add_rcu(kfd_processes_table, &process->kfd_processes,
+                       (uintptr_t)process->mm);
+
+       /* MMU notifier registration must be the last call that can fail
+        * because after this point we cannot unwind the process creation.
+        * After this point, mmu_notifier_put will trigger the cleanup by
+        * dropping the last process reference in the free_notifier.
+        */
+       mn = mmu_notifier_get(&kfd_process_mmu_notifier_ops, process->mm);
+       if (IS_ERR(mn)) {
+               err = PTR_ERR(mn);
                goto err_register_notifier;
+       }
+       BUG_ON(mn != &process->mmu_notifier);
 
        get_task_struct(process->lead_thread);
-       hash_add_rcu(kfd_processes_table, &process->kfd_processes,
-                       (uintptr_t)process->mm);
 
        return process;
 
 err_register_notifier:
+       hash_del_rcu(&process->kfd_processes);
        kfd_process_free_outstanding_kfd_bos(process);
        kfd_process_destroy_pdds(process);
 err_init_apertures:
-- 
2.17.1

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