[Intel-gfx] [PATCH] drm/i915: Allow dead vm to unbind vma's without lock.

[Maarten Lankhorst]

Op 28-01-2022 om 12:02 schreef Thomas Hellström (Intel):
>
> On 1/28/22 09:57, Maarten Lankhorst wrote:
>> i915_gem_vm_close may take the lock, and we currently have no better way
>> of handling this. At least for now, allow a path in which holding vm->mutex
>> is sufficient. This is the case, because the object destroy path will
>> forcefully take vm->mutex now.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>
> Reviewed-by: Thomas Hellstrom <thomas.hellstrom at linux.intel.com>
>
>
>> ---
>>   drivers/gpu/drm/i915/i915_vma.c | 15 +++++++++++++--
>>   1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
>> index b959e904c4d3..14a301c4069f 100644
>> --- a/drivers/gpu/drm/i915/i915_vma.c
>> +++ b/drivers/gpu/drm/i915/i915_vma.c
>> @@ -40,6 +40,17 @@
>>   #include "i915_vma.h"
>>   #include "i915_vma_resource.h"
>>   +static inline void assert_vma_held_evict(const struct i915_vma *vma)
>> +{
>> +    /*
>> +     * We may be forced to unbind when the vm is dead, to clean it up.
>> +     * This is the only exception to the requirement of the object lock
>> +     * being held.
>> +     */
>> +    if (atomic_read(&vma->vm->open))
>> +        assert_object_held_shared(vma->obj);
>> +}
>> +
>>   static struct kmem_cache *slab_vmas;
>>     static struct i915_vma *i915_vma_alloc(void)
>> @@ -1779,7 +1790,7 @@ struct dma_fence *__i915_vma_evict(struct i915_vma *vma, bool async)
>>       struct dma_fence *unbind_fence;
>>         GEM_BUG_ON(i915_vma_is_pinned(vma));
>> -    assert_object_held_shared(vma->obj);
>> +    assert_vma_held_evict(vma);
>>         if (i915_vma_is_map_and_fenceable(vma)) {
>>           /* Force a pagefault for domain tracking on next user access */
>> @@ -1846,7 +1857,7 @@ int __i915_vma_unbind(struct i915_vma *vma)
>>       int ret;
>>         lockdep_assert_held(&vma->vm->mutex);
>> -    assert_object_held_shared(vma->obj);
>> +    assert_vma_held_evict(vma);
>>         if (!drm_mm_node_allocated(&vma->node))
>>           return 0;

Thanks, pushed. Should fix alderlake DPT.