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SubjectRe: [PATCH 1/3] amdkfd: Don't clear *kfd2kgd on kfd_module_init
Am 21.12.2014 um 17:03 schrieb Oded Gabbay:
>
>
> On 12/21/2014 05:57 PM, Christian König wrote:
>>> There should be, but when the modules are compiled in, they are
>>> loaded based on
>>> link order only, if they are in the same group, and the groups are
>>> loaded by a
>>> pre-defined order.
>> Is that really still up to date? I've seen effort to change that
>> something like
>> 10+ years ago when Rusty reworked the module system. And it is
>> comming up on the
>> lists again from time to time.
> From what I can see in the Makefile rules, code and google, yes,
> that's still the situation. If someone will prove me wrong I will be
> more than happy to correct my code.
>>
>>> I don't want to move iommu before gpu, so I don't have a solution
>>> for the
>>> order between amdkfd and amd_iommu_v2.
>> Why not? That's still better than creating a kernel workqueue,
>> scheduling one
>> work item on it, rescheduling the task until everything is completed
>> and you can
>> continue.
> Because I don't know the consequences of moving an entire subsystem in
> front of another one. In addition, even if everyone agrees, I'm pretty
> sure that Linus won't be happy to do that in -rc stages. So maybe this
> is something to consider for 3.20 merge window, but I would still like
> to provide a solution for 3.19.

Yeah, true indeed. How about depending on everything being compiled as
module for 3.19 then? Still better than having such a hack in the driver
for as a temporary workaround for one release.

Christian.

>
> Oded
>>
>> Christian.
>>
>> Am 21.12.2014 um 14:24 schrieb Oded Gabbay:
>>>
>>>
>>> On 12/21/2014 03:06 PM, Oded Gabbay wrote:
>>>>
>>>>
>>>> On 12/21/2014 02:19 PM, Christian König wrote:
>>>>> Am 21.12.2014 um 12:34 schrieb Oded Gabbay:
>>>>>>
>>>>>>
>>>>>> On 12/21/2014 01:27 PM, Christian König wrote:
>>>>>>> Am 20.12.2014 um 21:46 schrieb Oded Gabbay:
>>>>>>>> When amdkfd and radeon are compiled inside the kernel image
>>>>>>>> (not as
>>>>>>>> modules),
>>>>>>>> radeon will load before amdkfd and will set *kfd2kgd to its
>>>>>>>> interface
>>>>>>>> structure. Therefore, we must not set *kfd2kgd to NULL when
>>>>>>>> amdkfd is loaded
>>>>>>>> because it will override radeon's initialization and cause
>>>>>>>> kernel BUG.
>>>>>>>>
>>>>>>>> Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
>>>>>>>
>>>>>>> You should probably rather fix the dependency between the two
>>>>>>> modules to
>>>>>>> get an
>>>>>>> determined load order instead of doing such nasty workarounds.
>>>>>>>
>>>>>>> Christian.
>>>>>>
>>>>>> The problem is that when modules are compiled inside the kernel,
>>>>>> there is NO
>>>>>> determined load order and there is no mechanism to enforce that.
>>>>>> If there
>>>>>> is/was such a mechanism, I would of course prefer to use it.
>>>>>
>>>>> There should be an determined order based on the symbol use,
>>>>> otherwise
>>>>> initializing most of the kernel modules wouldn't work as expected.
>>>>> For example
>>>>> radeon depends on the drm module must be loaded before radeon is
>>>>> loaded.
>>>> There should be, but when the modules are compiled in, they are
>>>> loaded based on
>>>> link order only, if they are in the same group, and the groups are
>>>> loaded by a
>>>> pre-defined order.
>>>> The groups are: pure, core, postcore, arch, subsys, fs, device
>>>> (which represents
>>>> all the modules) and late. See init.h
>>>>
>>>> So radeon, amdkfd and amd_iommu_v2 are all in device group, and in
>>>> the group
>>>> they are ordered by their link order.
>>>>
>>>> Yes, radeon loads after drm, because drm*.o are before radeon*.o in
>>>> the
>>>> Makefile. See
>>>> http://stackoverflow.com/questions/5669647/linux-order-of-statically-linked-module-loading
>>>>
>>>>
>>>>
>>>
>>> So I tried moving amdkfd inside the Makefile before radeon, and that
>>> made
>>> amdkfd load before radeon did. This solves my first problem - order
>>> between
>>> amdkfd and radeon. However, amd_iommu_v2 doesn't belong to the drm
>>> Makefile,
>>> and I don't want to move iommu before gpu, so I don't have a
>>> solution for the
>>> order between amdkfd and amd_iommu_v2.
>>>
>>> Oded
>>>>
>>>>
>>>>>
>>>>>>
>>>>>> Actually, I don't understand why the kernel doesn't enforce the
>>>>>> order
>>>>>> according to the use of exported symbols, like it does with modules.
>>>>>
>>>>> Yeah, that's indeed rather strange. There must be something in the
>>>>> amdkfd code
>>>>> which broke that somehow.
>>>> IMO, that's a far-fetched guess. Could you point to something more
>>>> specific ?
>>>>
>>>>>
>>>>> As far as I understand you the desired init order is radeon and
>>>>> amd_iommu_v2
>>>>> first and then amdkfd, right?
>>>> Actually no. The preferred order is amd_iommu_v2, amdkfd and radeon
>>>> last. This
>>>> is the order that happens when all three are built as modules. More
>>>> accurately,
>>>> radeon inits, but its init triggers amdkfd init, which triggers
>>>> amd_iommu_v2
>>>> init. So before radeon reaches its probe stage, all the modules were
>>>> initialized.
>>>>
>>>> So what happens when you boot with radeon,
>>>>> amd_iommu_v2 and amdkfd blacklisted for automatically load and
>>>>> only load amdkfd
>>>>> manually?
>>>> As said above, that's ok.
>>>>>
>>>>>> There will always be dependencies between kgd (radeon) and amdkfd
>>>>>> and between
>>>>>> amdkfd and amd_iommu_v2. I don't think I can eliminate those
>>>>>> dependencies, not
>>>>>> without a very complex solution. And the fact that this complex
>>>>>> solution
>>>>>> occurs only in a very specific use case (all modules compiled
>>>>>> in), makes me
>>>>>> less inclined to do that.
>>>>>>
>>>>>> So I don't see it as a "nasty workaround". I would call it just a
>>>>>> "workaround"
>>>>>> for a specific use case, which should be solved by a generic
>>>>>> solution to the
>>>>>> kernel enforcing load orders.
>>>>>
>>>>> The normal kernel module handling already should provide the
>>>>> correct init
>>>>> order,
>>>>> so I would still call this a rather nasty workaround because we
>>>>> couldn't find
>>>>> the underlying problem.
>>>> Well, the normal kernel module handling doesn't work when all
>>>> modules are
>>>> compiled in. I'm not a huge expert on this issue so I had Joerg
>>>> Roedel help me
>>>> analyze this (thanks Joerg) and he agreed that there is no
>>>> enforcement of order
>>>> in this case.
>>>>
>>>>>
>>>>> Christian.
>>>>>
>>>>>>
>>>>>> Oded
>>>>>>>
>>>>>>>> ---
>>>>>>>> drivers/gpu/drm/amd/amdkfd/kfd_module.c | 5 ++---
>>>>>>>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_module.c
>>>>>>>> b/drivers/gpu/drm/amd/amdkfd/kfd_module.c
>>>>>>>> index 95d5af1..236562f 100644
>>>>>>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_module.c
>>>>>>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_module.c
>>>>>>>> @@ -34,7 +34,7 @@
>>>>>>>> #define KFD_DRIVER_MINOR 7
>>>>>>>> #define KFD_DRIVER_PATCHLEVEL 0
>>>>>>>> -const struct kfd2kgd_calls *kfd2kgd;
>>>>>>>> +const struct kfd2kgd_calls *kfd2kgd = NULL;
>>>>>>>> static const struct kgd2kfd_calls kgd2kfd = {
>>>>>>>> .exit = kgd2kfd_exit,
>>>>>>>> .probe = kgd2kfd_probe,
>>>>>>>> @@ -84,14 +84,13 @@ EXPORT_SYMBOL(kgd2kfd_init);
>>>>>>>> void kgd2kfd_exit(void)
>>>>>>>> {
>>>>>>>> + kfd2kgd = NULL;
>>>>>>>> }
>>>>>>>> static int __init kfd_module_init(void)
>>>>>>>> {
>>>>>>>> int err;
>>>>>>>> - kfd2kgd = NULL;
>>>>>>>> -
>>>>>>>> /* Verify module parameters */
>>>>>>>> if ((sched_policy < KFD_SCHED_POLICY_HWS) ||
>>>>>>>> (sched_policy > KFD_SCHED_POLICY_NO_HWS)) {
>>>>>>>
>>>>>
>>>> _______________________________________________
>>>> dri-devel mailing list
>>>> dri-devel@lists.freedesktop.org
>>>> http://lists.freedesktop.org/mailman/listinfo/dri-devel
>>
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