Am 30.10.2017 um 17:23 schrieb Felix Kuehling:
> On 2017-10-28 10:44 AM, Christian König wrote:
>> Am 28.10.2017 um 01:35 schrieb Felix Kuehling:
>>> The kfd_process doesn't own a reference to the mm_struct, so it can
>>> disappear without warning even while the kfd_process still exists.
>>>
>>> Therefore, avoid dereferencing the kfd_process.mm pointer and make
>>> it opaque. Use get_task_mm to get a temporary reference to the mm
>>> when it's needed.
>>>
>>> v2: removed unnecessary WARN_ON
>>>
>>> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
>>> Reviewed-by: Oded Gabbay <oded.gabbay at gmail.com> (v1)
>>> ---
>>>  drivers/gpu/drm/amd/amdkfd/kfd_events.c | 19 +++++++++++++++----
>>>  drivers/gpu/drm/amd/amdkfd/kfd_priv.h   | 7 ++++++-
>>> Â drivers/gpu/drm/amd/amdkfd/kfd_process.c |Â 1 -
>>> Â 3 files changed, 21 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>>> b/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>>> index 944abfa..61ce547 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_events.c
>>> @@ -24,8 +24,8 @@
>>> Â #include <linux/slab.h>
>>> Â #include <linux/types.h>
>>> Â #include <linux/sched/signal.h>
>>> +#include <linux/sched/mm.h>
>>> Â #include <linux/uaccess.h>
>>> -#include <linux/mm.h>
>>> Â #include <linux/mman.h>
>>> Â #include <linux/memory.h>
>>> Â #include "kfd_priv.h"
>>> @@ -904,14 +904,24 @@ void kfd_signal_iommu_event(struct kfd_dev
>>> *dev, unsigned int pasid,
>>> Â Â Â Â Â Â * running so the lookup function returns a locked process.
>>> Â Â Â Â Â Â */
>>> Â Â Â Â Â struct kfd_process *p = kfd_lookup_process_by_pasid(pasid);
>>> +Â Â Â struct mm_struct *mm;
>>> Â Â Â Â Â Â if (!p)
>>> Â Â Â Â Â Â Â Â Â return; /* Presumably process exited. */
>>> Â +Â Â Â /* Take a safe reference to the mm_struct, which may otherwise
>>> +Â Â Â Â * disappear even while the kfd_process is still referenced.
>>> +Â Â Â Â */
>>> +Â Â Â mm = get_task_mm(p->lead_thread);
>>> +Â Â Â if (!mm) {
>>> +Â Â Â Â Â Â Â mutex_unlock(&p->mutex);
>>> +Â Â Â Â Â Â Â return; /* Process is exiting */
>>> +Â Â Â }
>>> +
>>> Â Â Â Â Â memset(&memory_exception_data, 0, sizeof(memory_exception_data));
>>> Â -Â Â Â down_read(&p->mm->mmap_sem);
>>> -Â Â Â vma = find_vma(p->mm, address);
>>> +Â Â Â down_read(&mm->mmap_sem);
>>> +Â Â Â vma = find_vma(mm, address);
>>> Â Â Â Â Â Â memory_exception_data.gpu_id = dev->id;
>>> Â Â Â Â Â memory_exception_data.va = address;
>>> @@ -937,7 +947,8 @@ void kfd_signal_iommu_event(struct kfd_dev *dev,
>>> unsigned int pasid,
>>> Â Â Â Â Â Â Â Â Â }
>>> Â Â Â Â Â }
>>> Â -Â Â Â up_read(&p->mm->mmap_sem);
>>> +Â Â Â up_read(&mm->mmap_sem);
>>> +Â Â Â mmput(mm);
>>> Â Â Â Â Â Â mutex_lock(&p->event_mutex);
>>> Â diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> index 7d86ec9..1a483a7 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> @@ -494,7 +494,12 @@ struct kfd_process {
>>> Â Â Â Â Â Â */
>>> Â Â Â Â Â struct hlist_node kfd_processes;
>>> Â -Â Â Â struct mm_struct *mm;
>>> +Â Â Â /*
>>> +Â Â Â Â * Opaque pointer to mm_struct. We don't hold a reference to
>>> +Â Â Â Â * it so it should never be dereferenced from here. This is
>>> +Â Â Â Â * only used for looking up processes by their mm.
>>> +Â Â Â Â */
>>> +Â Â Â void *mm;
>> Using a void* here still doesn't look like the right thing to do.
> For added context, this is how it's used:
>
> static struct kfd_process *create_process(const struct task_struct *thread)
> {
> ...
> process->mm = thread->mm;
> ...
> hash_add_rcu(kfd_processes_table, &process->kfd_processes,
> (uintptr_t)process->mm);
> ...
> }
>
> static struct kfd_process *find_process_by_mm(const struct mm_struct *mm)
> {
> struct kfd_process *process;
>
> hash_for_each_possible_rcu(kfd_processes_table, process,
> kfd_processes, (uintptr_t)mm)
> if (process->mm == mm)
> return process;
>
> return NULL;
> }
In this case I would make p->mm a uintptr_t and not void*. I would use
void* only if you really don't know what pointer it is.
Anyway the patch is fine with me as it is, just wanted to understand
what's happening here.
Regards,
Christian.
>
>
>>> Â Â Â Â Â Â struct mutex mutex;
>>> Â diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> index 3ccb3b5..695fa2a 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
>>> @@ -200,7 +200,6 @@ static void kfd_process_destroy_delayed(struct
>>> rcu_head *rcu)
>>> Â Â Â Â Â struct kfd_process *p;
>>> Â Â Â Â Â Â p = container_of(rcu, struct kfd_process, rcu);
>>> -Â Â Â WARN_ON(atomic_read(&p->mm->mm_count) <= 0);
>>> Â Â Â Â Â Â mmdrop(p->mm);
>> If you are concerned that p->mm is used after this just set it to NULL.
> I'm not concerned about it.
>
> Regards,
> Â Felix
>
>> Regards,
>> Christian.
>>
>>>
>>
