This small patch-set, was created to solve the bug described at
https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
trying use amdkfd driver on Kaveri). It replaces the previous patch-set called
[PATCH 0/3] Use workqueue for device init in amdkfd
(http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html)
That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
inside the kernel (not as modules). In that case, the correct loading
order, as determined by the exported symbol used by each driver, is
not enforced anymore and the kernel loads them based on who was linked
first. That makes radeon load first, amdkfd second and amd_iommu_v2
third.
Because the initialization of a device in amdkfd is initiated by radeon,
and can only be completed if amdkfd and amd_iommu_v2 were loaded and
initialized, then in the case mentioned above, this initalization fails
and there is a kernel panic as some pointers are not initialized but
used nontheless.
To solve this bug, this patch-set moves iommu/ before gpu/ in drivers/Makefile
and also moves amdkfd/ before radeon/ in drivers/gpu/drm/Makefile.
The rationale is that in general, AMD GPU devices are dependent on AMD IOMMU
controller functionality to allow the GPU to access a process's virtual memory
address space, without the need for pinning the memory. That's why it makes
sense to initialize the iommu/ subsystem ahead of the gpu/ subsystem.
Oded
Oded Gabbay (2):
drivers: Move iommu/ before gpu/ in Makefile
drm: Put amdkfd before radeon in drm Makefile
drivers/Makefile | 6 ++++--
drivers/gpu/drm/Makefile | 2 +-
2 files changed, 5 insertions(+), 3 deletions(-)
--
1.9.1
AMD GPU devices are dependent on AMD IOMMU controller functionality to allow
the GPU to access a process's virtual memory address space, without the need
for pinning the memory.
This patch changes the order in the drivers makefile, so iommu/ subsystem is
linked before gpu/ subsystem. That way, if the gpu and iommu drivers are
compiled inside the kernel image (not as modules), the correct order of device
loading is still maintained (iommu module is loaded before gpu module).
Signed-off-by: Oded Gabbay <[email protected]>
---
drivers/Makefile | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/Makefile b/drivers/Makefile
index ebee555..106200f 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -50,7 +50,10 @@ obj-$(CONFIG_RESET_CONTROLLER) += reset/
obj-y += tty/
obj-y += char/
-# gpu/ comes after char for AGP vs DRM startup
+# iommu/ comes before gpu as gpu are using iommu controllers
+obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
+
+# gpu/ comes after char for AGP vs DRM startup and after iommu
obj-y += gpu/
obj-$(CONFIG_CONNECTOR) += connector/
@@ -141,7 +144,6 @@ obj-y += clk/
obj-$(CONFIG_MAILBOX) += mailbox/
obj-$(CONFIG_HWSPINLOCK) += hwspinlock/
-obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
obj-$(CONFIG_REMOTEPROC) += remoteproc/
obj-$(CONFIG_RPMSG) += rpmsg/
--
1.9.1
When amdkfd and radeon are compiled inside the kernel image (not as modules),
radeon will load before amdkfd, which will cause a bug when radeon will probe
the GPUs.
When the two drivers are compiled as modules, amdkfd is loaded after radeon is
loaded but before radeon starts probing the GPUs. This is done because radeon
loads the amdkfd module through symbol_request function.
This patch makes amdkfd load before radeon when they are both compiled inside
the kernel image, which makes the behavior similar to the case when they are
modules, and prevents the kernel bug.
Signed-off-by: Oded Gabbay <[email protected]>
---
drivers/gpu/drm/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 66e4039..e620807 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -37,6 +37,7 @@ obj-$(CONFIG_DRM_MIPI_DSI) += drm_mipi_dsi.o
obj-$(CONFIG_DRM_TTM) += ttm/
obj-$(CONFIG_DRM_TDFX) += tdfx/
obj-$(CONFIG_DRM_R128) += r128/
+obj-$(CONFIG_HSA_AMD) += amd/amdkfd/
obj-$(CONFIG_DRM_RADEON)+= radeon/
obj-$(CONFIG_DRM_MGA) += mga/
obj-$(CONFIG_DRM_I810) += i810/
@@ -67,4 +68,3 @@ obj-$(CONFIG_DRM_IMX) += imx/
obj-y += i2c/
obj-y += panel/
obj-y += bridge/
-obj-$(CONFIG_HSA_AMD) += amd/amdkfd/
--
1.9.1
For this series: Reviewed-by: Christian K?nig <[email protected]>
Am 22.12.2014 um 12:07 schrieb Oded Gabbay:
> This small patch-set, was created to solve the bug described at
> https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
> trying use amdkfd driver on Kaveri). It replaces the previous patch-set called
> [PATCH 0/3] Use workqueue for device init in amdkfd
> (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html)
>
> That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
> inside the kernel (not as modules). In that case, the correct loading
> order, as determined by the exported symbol used by each driver, is
> not enforced anymore and the kernel loads them based on who was linked
> first. That makes radeon load first, amdkfd second and amd_iommu_v2
> third.
>
> Because the initialization of a device in amdkfd is initiated by radeon,
> and can only be completed if amdkfd and amd_iommu_v2 were loaded and
> initialized, then in the case mentioned above, this initalization fails
> and there is a kernel panic as some pointers are not initialized but
> used nontheless.
>
> To solve this bug, this patch-set moves iommu/ before gpu/ in drivers/Makefile
> and also moves amdkfd/ before radeon/ in drivers/gpu/drm/Makefile.
>
> The rationale is that in general, AMD GPU devices are dependent on AMD IOMMU
> controller functionality to allow the GPU to access a process's virtual memory
> address space, without the need for pinning the memory. That's why it makes
> sense to initialize the iommu/ subsystem ahead of the gpu/ subsystem.
>
> Oded
>
> Oded Gabbay (2):
> drivers: Move iommu/ before gpu/ in Makefile
> drm: Put amdkfd before radeon in drm Makefile
>
> drivers/Makefile | 6 ++++--
> drivers/gpu/drm/Makefile | 2 +-
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
Hello Linus,
Dave Airlie asked me to send this patch to you for review.
See link below for cover-letter for this patch that explains the background a
bit more:
http://lists.freedesktop.org/archives/dri-devel/2014-December/074452.html
Thanks,
Oded
On 12/22/2014 01:07 PM, Oded Gabbay wrote:
> AMD GPU devices are dependent on AMD IOMMU controller functionality to allow
> the GPU to access a process's virtual memory address space, without the need
> for pinning the memory.
>
> This patch changes the order in the drivers makefile, so iommu/ subsystem is
> linked before gpu/ subsystem. That way, if the gpu and iommu drivers are
> compiled inside the kernel image (not as modules), the correct order of device
> loading is still maintained (iommu module is loaded before gpu module).
>
> Signed-off-by: Oded Gabbay <[email protected]>
> ---
> drivers/Makefile | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/Makefile b/drivers/Makefile
> index ebee555..106200f 100644
> --- a/drivers/Makefile
> +++ b/drivers/Makefile
> @@ -50,7 +50,10 @@ obj-$(CONFIG_RESET_CONTROLLER) += reset/
> obj-y += tty/
> obj-y += char/
>
> -# gpu/ comes after char for AGP vs DRM startup
> +# iommu/ comes before gpu as gpu are using iommu controllers
> +obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
> +
> +# gpu/ comes after char for AGP vs DRM startup and after iommu
> obj-y += gpu/
>
> obj-$(CONFIG_CONNECTOR) += connector/
> @@ -141,7 +144,6 @@ obj-y += clk/
>
> obj-$(CONFIG_MAILBOX) += mailbox/
> obj-$(CONFIG_HWSPINLOCK) += hwspinlock/
> -obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
> obj-$(CONFIG_REMOTEPROC) += remoteproc/
> obj-$(CONFIG_RPMSG) += rpmsg/
>
>
On Mon, Dec 22, 2014 at 01:07:13PM +0200, Oded Gabbay wrote:
> This small patch-set, was created to solve the bug described at
> https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
> trying use amdkfd driver on Kaveri). It replaces the previous patch-set called
> [PATCH 0/3] Use workqueue for device init in amdkfd
> (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html)
>
> That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
> inside the kernel (not as modules). In that case, the correct loading
> order, as determined by the exported symbol used by each driver, is
> not enforced anymore and the kernel loads them based on who was linked
> first. That makes radeon load first, amdkfd second and amd_iommu_v2
> third.
>
> Because the initialization of a device in amdkfd is initiated by radeon,
> and can only be completed if amdkfd and amd_iommu_v2 were loaded and
> initialized, then in the case mentioned above, this initalization fails
> and there is a kernel panic as some pointers are not initialized but
> used nontheless.
>
> To solve this bug, this patch-set moves iommu/ before gpu/ in drivers/Makefile
> and also moves amdkfd/ before radeon/ in drivers/gpu/drm/Makefile.
>
> The rationale is that in general, AMD GPU devices are dependent on AMD IOMMU
> controller functionality to allow the GPU to access a process's virtual memory
> address space, without the need for pinning the memory. That's why it makes
> sense to initialize the iommu/ subsystem ahead of the gpu/ subsystem.
I strongly object to this patch set. This makes assumptions about how
the build system influences probe order. That's bad because seemingly
unrelated changes could easily break this in the future.
We already have ways to solve this kind of dependency (driver probe
deferral), and I think you should be using it to solve this particular
problem rather than some linking order hack.
Coincidentally there's a separate thread currently going on that deals
with IOMMUs and probe order. The solution being worked on is currently
somewhat ARM-specific, so adding a couple of folks for visibility. It
looks like we're going to need something more generic since this is a
problem that even the "big" architectures need to solve.
Thierry
On Tue, Dec 23, 2014 at 4:09 AM, Oded Gabbay <[email protected]> wrote:
> Hello Linus,
> Dave Airlie asked me to send this patch to you for review.
I'm not entirely happy about the fix, since we generally *should*
order things by the different init-levels, but we've done the link
order thing before, and I guess it's acceptable as a band-aid, even if
it's not really how things are supposed to be done.
Linus
Hi Thierry,
On Thursday 25 December 2014 14:20:59 Thierry Reding wrote:
> On Mon, Dec 22, 2014 at 01:07:13PM +0200, Oded Gabbay wrote:
> > This small patch-set, was created to solve the bug described at
> > https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
> > trying use amdkfd driver on Kaveri). It replaces the previous patch-set
> > called [PATCH 0/3] Use workqueue for device init in amdkfd
> > (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html
> > )
> >
> > That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
> > inside the kernel (not as modules). In that case, the correct loading
> > order, as determined by the exported symbol used by each driver, is
> > not enforced anymore and the kernel loads them based on who was linked
> > first. That makes radeon load first, amdkfd second and amd_iommu_v2
> > third.
> >
> > Because the initialization of a device in amdkfd is initiated by radeon,
> > and can only be completed if amdkfd and amd_iommu_v2 were loaded and
> > initialized, then in the case mentioned above, this initalization fails
> > and there is a kernel panic as some pointers are not initialized but
> > used nontheless.
> >
> > To solve this bug, this patch-set moves iommu/ before gpu/ in
> > drivers/Makefile and also moves amdkfd/ before radeon/ in
> > drivers/gpu/drm/Makefile.
> >
> > The rationale is that in general, AMD GPU devices are dependent on AMD
> > IOMMU controller functionality to allow the GPU to access a process's
> > virtual memory address space, without the need for pinning the memory.
> > That's why it makes sense to initialize the iommu/ subsystem ahead of the
> > gpu/ subsystem.
>
> I strongly object to this patch set. This makes assumptions about how
> the build system influences probe order. That's bad because seemingly
> unrelated changes could easily break this in the future.
>
> We already have ways to solve this kind of dependency (driver probe
> deferral), and I think you should be using it to solve this particular
> problem rather than some linking order hack.
While I agree with you that probe deferral is the way to go, I believe linkage
ordering can still be used as an optimization to avoid deferring probe in the
most common cases. I'm thus not opposed to moving iommu/ earlier in link order
(provided we can properly test for side effects, as the jump is pretty large),
but not as a replacement for probe deferral.
> Coincidentally there's a separate thread currently going on that deals
> with IOMMUs and probe order. The solution being worked on is currently
> somewhat ARM-specific, so adding a couple of folks for visibility. It
> looks like we're going to need something more generic since this is a
> problem that even the "big" architectures need to solve.
--
Regards,
Laurent Pinchart
On 12/26/2014 11:19 AM, Laurent Pinchart wrote:
> Hi Thierry,
>
> On Thursday 25 December 2014 14:20:59 Thierry Reding wrote:
>> On Mon, Dec 22, 2014 at 01:07:13PM +0200, Oded Gabbay wrote:
>>> This small patch-set, was created to solve the bug described at
>>> https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
>>> trying use amdkfd driver on Kaveri). It replaces the previous patch-set
>>> called [PATCH 0/3] Use workqueue for device init in amdkfd
>>> (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.html
>>> )
>>>
>>> That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
>>> inside the kernel (not as modules). In that case, the correct loading
>>> order, as determined by the exported symbol used by each driver, is
>>> not enforced anymore and the kernel loads them based on who was linked
>>> first. That makes radeon load first, amdkfd second and amd_iommu_v2
>>> third.
>>>
>>> Because the initialization of a device in amdkfd is initiated by radeon,
>>> and can only be completed if amdkfd and amd_iommu_v2 were loaded and
>>> initialized, then in the case mentioned above, this initalization fails
>>> and there is a kernel panic as some pointers are not initialized but
>>> used nontheless.
>>>
>>> To solve this bug, this patch-set moves iommu/ before gpu/ in
>>> drivers/Makefile and also moves amdkfd/ before radeon/ in
>>> drivers/gpu/drm/Makefile.
>>>
>>> The rationale is that in general, AMD GPU devices are dependent on AMD
>>> IOMMU controller functionality to allow the GPU to access a process's
>>> virtual memory address space, without the need for pinning the memory.
>>> That's why it makes sense to initialize the iommu/ subsystem ahead of the
>>> gpu/ subsystem.
>>
>> I strongly object to this patch set. This makes assumptions about how
>> the build system influences probe order. That's bad because seemingly
>> unrelated changes could easily break this in the future.
>>
>> We already have ways to solve this kind of dependency (driver probe
>> deferral), and I think you should be using it to solve this particular
>> problem rather than some linking order hack.
>
> While I agree with you that probe deferral is the way to go, I believe linkage
> ordering can still be used as an optimization to avoid deferring probe in the
> most common cases. I'm thus not opposed to moving iommu/ earlier in link order
> (provided we can properly test for side effects, as the jump is pretty large),
> but not as a replacement for probe deferral.
My thoughts exactly. If this was some extreme use case, than it would be
justified to solve it with probe deferral. But I think that for most common
cases, GPU are dependent on IOMMU and *not* vice-versa.
BTW, my first try at solving this was to use probe deferral (using workqueue),
but the feedback I got from Christian and Dave was that moving iommu/ linkage
before gpu/ was a much more simpler solution.
In addition, Linus said he doesn't object to this "band-aid". See:
https://lkml.org/lkml/2014/12/25/152
Oded
>
>> Coincidentally there's a separate thread currently going on that deals
>> with IOMMUs and probe order. The solution being worked on is currently
>> somewhat ARM-specific, so adding a couple of folks for visibility. It
>> looks like we're going to need something more generic since this is a
>> problem that even the "big" architectures need to solve.
>
Hi Oded,
On Sunday 28 December 2014 13:36:50 Oded Gabbay wrote:
> On 12/26/2014 11:19 AM, Laurent Pinchart wrote:
> > On Thursday 25 December 2014 14:20:59 Thierry Reding wrote:
> >> On Mon, Dec 22, 2014 at 01:07:13PM +0200, Oded Gabbay wrote:
> >>> This small patch-set, was created to solve the bug described at
> >>> https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
> >>> trying use amdkfd driver on Kaveri). It replaces the previous patch-set
> >>> called [PATCH 0/3] Use workqueue for device init in amdkfd
> >>> (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.ht
> >>> ml)
> >>>
> >>> That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
> >>> inside the kernel (not as modules). In that case, the correct loading
> >>> order, as determined by the exported symbol used by each driver, is
> >>> not enforced anymore and the kernel loads them based on who was linked
> >>> first. That makes radeon load first, amdkfd second and amd_iommu_v2
> >>> third.
> >>>
> >>> Because the initialization of a device in amdkfd is initiated by radeon,
> >>> and can only be completed if amdkfd and amd_iommu_v2 were loaded and
> >>> initialized, then in the case mentioned above, this initalization fails
> >>> and there is a kernel panic as some pointers are not initialized but
> >>> used nontheless.
> >>>
> >>> To solve this bug, this patch-set moves iommu/ before gpu/ in
> >>> drivers/Makefile and also moves amdkfd/ before radeon/ in
> >>> drivers/gpu/drm/Makefile.
> >>>
> >>> The rationale is that in general, AMD GPU devices are dependent on AMD
> >>> IOMMU controller functionality to allow the GPU to access a process's
> >>> virtual memory address space, without the need for pinning the memory.
> >>> That's why it makes sense to initialize the iommu/ subsystem ahead of
> >>> the gpu/ subsystem.
> >>
> >> I strongly object to this patch set. This makes assumptions about how
> >> the build system influences probe order. That's bad because seemingly
> >> unrelated changes could easily break this in the future.
> >>
> >> We already have ways to solve this kind of dependency (driver probe
> >> deferral), and I think you should be using it to solve this particular
> >> problem rather than some linking order hack.
> >
> > While I agree with you that probe deferral is the way to go, I believe
> > linkage ordering can still be used as an optimization to avoid deferring
> > probe in the most common cases. I'm thus not opposed to moving iommu/
> > earlier in link order (provided we can properly test for side effects, as
> > the jump is pretty large), but not as a replacement for probe deferral.
>
> My thoughts exactly. If this was some extreme use case, than it would be
> justified to solve it with probe deferral. But I think that for most common
> cases, GPU are dependent on IOMMU and *not* vice-versa.
>
> BTW, my first try at solving this was to use probe deferral (using
> workqueue), but the feedback I got from Christian and Dave was that moving
> iommu/ linkage before gpu/ was a much more simpler solution.
To clarify my position, I believe changing the link order can be a worthwhile
optimization, but I'm uncertain about the long term viability of that change
as a fix. Probe deferral has been introduced because not all probe ordering
issues can be fixed through link ordering, so we should fix the problem
properly.
This being said, if modifying the link order can help for now without
introducing negative side effects, it would only postpone the real fix, so I'm
not opposed to it.
> In addition, Linus said he doesn't object to this "band-aid". See:
> https://lkml.org/lkml/2014/12/25/152
>
> Oded
>
> >> Coincidentally there's a separate thread currently going on that deals
> >> with IOMMUs and probe order. The solution being worked on is currently
> >> somewhat ARM-specific, so adding a couple of folks for visibility. It
> >> looks like we're going to need something more generic since this is a
> >> problem that even the "big" architectures need to solve.
--
Regards,
Laurent Pinchart
Am 29.12.2014 um 09:16 schrieb Laurent Pinchart:
> Hi Oded,
>
> On Sunday 28 December 2014 13:36:50 Oded Gabbay wrote:
>> On 12/26/2014 11:19 AM, Laurent Pinchart wrote:
>>> On Thursday 25 December 2014 14:20:59 Thierry Reding wrote:
>>>> On Mon, Dec 22, 2014 at 01:07:13PM +0200, Oded Gabbay wrote:
>>>>> This small patch-set, was created to solve the bug described at
>>>>> https://bugzilla.kernel.org/show_bug.cgi?id=89661 (Kernel panic when
>>>>> trying use amdkfd driver on Kaveri). It replaces the previous patch-set
>>>>> called [PATCH 0/3] Use workqueue for device init in amdkfd
>>>>> (http://lists.freedesktop.org/archives/dri-devel/2014-December/074401.ht
>>>>> ml)
>>>>>
>>>>> That bug appears only when radeon, amdkfd and amd_iommu_v2 are compiled
>>>>> inside the kernel (not as modules). In that case, the correct loading
>>>>> order, as determined by the exported symbol used by each driver, is
>>>>> not enforced anymore and the kernel loads them based on who was linked
>>>>> first. That makes radeon load first, amdkfd second and amd_iommu_v2
>>>>> third.
>>>>>
>>>>> Because the initialization of a device in amdkfd is initiated by radeon,
>>>>> and can only be completed if amdkfd and amd_iommu_v2 were loaded and
>>>>> initialized, then in the case mentioned above, this initalization fails
>>>>> and there is a kernel panic as some pointers are not initialized but
>>>>> used nontheless.
>>>>>
>>>>> To solve this bug, this patch-set moves iommu/ before gpu/ in
>>>>> drivers/Makefile and also moves amdkfd/ before radeon/ in
>>>>> drivers/gpu/drm/Makefile.
>>>>>
>>>>> The rationale is that in general, AMD GPU devices are dependent on AMD
>>>>> IOMMU controller functionality to allow the GPU to access a process's
>>>>> virtual memory address space, without the need for pinning the memory.
>>>>> That's why it makes sense to initialize the iommu/ subsystem ahead of
>>>>> the gpu/ subsystem.
>>>> I strongly object to this patch set. This makes assumptions about how
>>>> the build system influences probe order. That's bad because seemingly
>>>> unrelated changes could easily break this in the future.
>>>>
>>>> We already have ways to solve this kind of dependency (driver probe
>>>> deferral), and I think you should be using it to solve this particular
>>>> problem rather than some linking order hack.
>>> While I agree with you that probe deferral is the way to go, I believe
>>> linkage ordering can still be used as an optimization to avoid deferring
>>> probe in the most common cases. I'm thus not opposed to moving iommu/
>>> earlier in link order (provided we can properly test for side effects, as
>>> the jump is pretty large), but not as a replacement for probe deferral.
>> My thoughts exactly. If this was some extreme use case, than it would be
>> justified to solve it with probe deferral. But I think that for most common
>> cases, GPU are dependent on IOMMU and *not* vice-versa.
Fixing this through deferred probing sounds like the correct long term
solution to me as well.
But what Thierry is referring to here is probably the approach of
returning -EAGAIN from the probe method (at least that was the last
status when I looked into this).
The problem with this approach is the interface design between radeon
and amdkfd. amdkfd simply doesn't have a probe method which gets called
when the hardware is detected and can return -EAGAIN. Instead amdkfd is
called by radeon after hardware initialization when it is way to late
for such a thing.
>>
>> BTW, my first try at solving this was to use probe deferral (using
>> workqueue), but the feedback I got from Christian and Dave was that moving
>> iommu/ linkage before gpu/ was a much more simpler solution.
> To clarify my position, I believe changing the link order can be a worthwhile
> optimization, but I'm uncertain about the long term viability of that change
> as a fix. Probe deferral has been introduced because not all probe ordering
> issues can be fixed through link ordering, so we should fix the problem
> properly.
>
> This being said, if modifying the link order can help for now without
> introducing negative side effects, it would only postpone the real fix, so I'm
> not opposed to it.
Yeah, that sounds like the right approach to me as well. In general I
would prefer that modules compiled into the kernel load by the order of
their symbol dependency just like standalone modules do.
That's what Rusty proposed more than 10 years ago when he reworked the
module system and I'm actually not sure why it was never done this way.
I can only find the initial patch to do so in the mail history, but not
why it was rejected.
Regards,
Christian.
>
>> In addition, Linus said he doesn't object to this "band-aid". See:
>> https://lkml.org/lkml/2014/12/25/152
>>
>> Oded
>>
>>>> Coincidentally there's a separate thread currently going on that deals
>>>> with IOMMUs and probe order. The solution being worked on is currently
>>>> somewhat ARM-specific, so adding a couple of folks for visibility. It
>>>> looks like we're going to need something more generic since this is a
>>>> problem that even the "big" architectures need to solve.