[PATCH] remoteproc: Remove null character write of shared mem

[PATCH] remoteproc: Remove null character write of shared mem

[Jitendra Sharma]

remoteproc is writing '\0' in the shared mem region. This
region is shared among multiple clients that are also trying
to read. Hence they miss first character.

Remove this null character write, as this mem area is
supposed to be Read only.

Further during every subsystem reboot, this region is
initialized with default, hence no need to write this
region.

Signed-off-by: Jitendra Sharma <shajit@codeaurora.org>
---
 drivers/remoteproc/qcom_adsp_pil.c | 3 ---
 drivers/remoteproc/qcom_q6v5_pil.c | 3 ---
 drivers/remoteproc/qcom_wcnss.c    | 3 ---
 3 files changed, 9 deletions(-)

diff --git a/drivers/remoteproc/qcom_adsp_pil.c b/drivers/remoteproc/qcom_adsp_pil.c
index 373c167..4a2ee6c 100644
--- a/drivers/remoteproc/qcom_adsp_pil.c
+++ b/drivers/remoteproc/qcom_adsp_pil.c
@@ -201,9 +201,6 @@ static irqreturn_t adsp_fatal_interrupt(int irq, void *dev)
 
 	rproc_report_crash(adsp->rproc, RPROC_FATAL_ERROR);
 
-	if (!IS_ERR(msg))
-		msg[0] = '\0';
-
 	return IRQ_HANDLED;
 }
 
diff --git a/drivers/remoteproc/qcom_q6v5_pil.c b/drivers/remoteproc/qcom_q6v5_pil.c
index b4e5e72..f51e143 100644
--- a/drivers/remoteproc/qcom_q6v5_pil.c
+++ b/drivers/remoteproc/qcom_q6v5_pil.c
@@ -959,9 +959,6 @@ static irqreturn_t q6v5_fatal_interrupt(int irq, void *dev)
 
 	rproc_report_crash(qproc->rproc, RPROC_FATAL_ERROR);
 
-	if (!IS_ERR(msg))
-		msg[0] = '\0';
-
 	return IRQ_HANDLED;
 }
 
diff --git a/drivers/remoteproc/qcom_wcnss.c b/drivers/remoteproc/qcom_wcnss.c
index 3f06092..043f3d3 100644
--- a/drivers/remoteproc/qcom_wcnss.c
+++ b/drivers/remoteproc/qcom_wcnss.c
@@ -332,9 +332,6 @@ static irqreturn_t wcnss_fatal_interrupt(int irq, void *dev)
 
 	rproc_report_crash(wcnss->rproc, RPROC_FATAL_ERROR);
 
-	if (!IS_ERR(msg))
-		msg[0] = '\0';
-
 	return IRQ_HANDLED;
 }
 
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH] remoteproc: Remove null character write of shared mem

[Bjorn Andersson]

On Wed 07 Feb 05:22 PST 2018, Jitendra Sharma wrote:

> remoteproc is writing '\0' in the shared mem region. This
> region is shared among multiple clients that are also trying
> to read. Hence they miss first character.
> 
> Remove this null character write, as this mem area is
> supposed to be Read only.
> 
> Further during every subsystem reboot, this region is
> initialized with default, hence no need to write this
> region.

Thanks for your patch Jitendra!

The write was removed from the downstream kernel in msm-4.9, late last
year. Can you please confirm that you describe here is valid for
platforms supported prior to this change as well?

E.g. is what you're describing true for wcnss on 8064, adsp on 8974 and
mpss on 8916?

Regards,
Bjorn

Re: [PATCH] remoteproc: Remove null character write of shared mem

[Jitendra Sharma]

Hi Bjorn,


On 2/7/2018 8:57 PM, Bjorn Andersson wrote:
> On Wed 07 Feb 05:22 PST 2018, Jitendra Sharma wrote:
>
>> remoteproc is writing '\0' in the shared mem region. This
>> region is shared among multiple clients that are also trying
>> to read. Hence they miss first character.
>>
>> Remove this null character write, as this mem area is
>> supposed to be Read only.
>>
>> Further during every subsystem reboot, this region is
>> initialized with default, hence no need to write this
>> region.
> Thanks for your patch Jitendra!
>
> The write was removed from the downstream kernel in msm-4.9, late last
> year. Can you please confirm that you describe here is valid for
> platforms supported prior to this change as well?
>
> E.g. is what you're describing true for wcnss on 8064, adsp on 8974 and
> mpss on 8916?
To provide a history.
We got a internal request, where during subsystem crash/restart, in our 
recovery path, we try to get the cause of crash by reading shared memory 
region.
But, because in recovery path we write null to first character of shared 
memory string. So, any other client which in the meantime try to dump 
the crash region will miss first character of crash region.
For example: actual "err_crash_reason " will be read by other interested 
clients as "rr_crash_reason"

Now as this piece of code is present since long 3.10,3.18,4.4 time, so 
we were not sure of this snippet's reason of existence. Here, initially 
we tried to find out reason for this null write, where we guessed this 
snippet is lying there to ensure, that across subsequent crashes, we 
always get a new updated reason/string(as we are writing null to first 
character of shared mem) and not some older stale string.

But this understanding was rejected by subsystem owners saying that 
crash reason, shared memory item is re-initialized at non-HLOS bootup so 
it will get clear automatically.Hence, there is no need to write null 
character.

So, because of above reason, we could say that this snippet is causing a 
bug and should be fixed and this change should be valid for any platform.
>
> Regards,
> Bjorn

Re: [PATCH] remoteproc: Remove null character write of shared mem

[Bjorn Andersson]

On Thu 08 Feb 01:12 PST 2018, Jitendra Sharma wrote:

> Hi Bjorn,
> 
> 
> On 2/7/2018 8:57 PM, Bjorn Andersson wrote:
> > On Wed 07 Feb 05:22 PST 2018, Jitendra Sharma wrote:
> > 
> > > remoteproc is writing '\0' in the shared mem region. This
> > > region is shared among multiple clients that are also trying
> > > to read. Hence they miss first character.
> > > 
> > > Remove this null character write, as this mem area is
> > > supposed to be Read only.
> > > 
> > > Further during every subsystem reboot, this region is
> > > initialized with default, hence no need to write this
> > > region.
> > Thanks for your patch Jitendra!
> > 
> > The write was removed from the downstream kernel in msm-4.9, late last
> > year. Can you please confirm that you describe here is valid for
> > platforms supported prior to this change as well?
> > 
> > E.g. is what you're describing true for wcnss on 8064, adsp on 8974 and
> > mpss on 8916?
> To provide a history.
> We got a internal request, where during subsystem crash/restart, in our
> recovery path, we try to get the cause of crash by reading shared memory
> region.
> But, because in recovery path we write null to first character of shared
> memory string. So, any other client which in the meantime try to dump the
> crash region will miss first character of crash region.
> For example: actual "err_crash_reason " will be read by other interested
> clients as "rr_crash_reason"
> 
> Now as this piece of code is present since long 3.10,3.18,4.4 time, so we
> were not sure of this snippet's reason of existence. Here, initially we
> tried to find out reason for this null write, where we guessed this snippet
> is lying there to ensure, that across subsequent crashes, we always get a
> new updated reason/string(as we are writing null to first character of
> shared mem) and not some older stale string.
> 
> But this understanding was rejected by subsystem owners saying that crash
> reason, shared memory item is re-initialized at non-HLOS bootup so it will
> get clear automatically.Hence, there is no need to write null character.
> 
> So, because of above reason, we could say that this snippet is causing a bug
> and should be fixed and this change should be valid for any platform.

Thanks for investigating this and letting me know.

As you say the only time this had the potential to be a problem would be
if we have a fatal error with a message followed by a crash that doesn't
fill out the message - in this case we could have read the old message.

I have merged your "v1" patch - which as it's the second version of the
patch, should be titled v2.

Regards,
Bjorn

Re: [PATCH] remoteproc: Remove null character write of shared mem

[Jitendra Sharma]

On 2/13/2018 12:09 AM, Bjorn Andersson wrote:
> On Thu 08 Feb 01:12 PST 2018, Jitendra Sharma wrote:
>
>> Hi Bjorn,
>>
>>
>> On 2/7/2018 8:57 PM, Bjorn Andersson wrote:
>>> On Wed 07 Feb 05:22 PST 2018, Jitendra Sharma wrote:
>>>
>>>> remoteproc is writing '\0' in the shared mem region. This
>>>> region is shared among multiple clients that are also trying
>>>> to read. Hence they miss first character.
>>>>
>>>> Remove this null character write, as this mem area is
>>>> supposed to be Read only.
>>>>
>>>> Further during every subsystem reboot, this region is
>>>> initialized with default, hence no need to write this
>>>> region.
>>> Thanks for your patch Jitendra!
>>>
>>> The write was removed from the downstream kernel in msm-4.9, late last
>>> year. Can you please confirm that you describe here is valid for
>>> platforms supported prior to this change as well?
>>>
>>> E.g. is what you're describing true for wcnss on 8064, adsp on 8974 and
>>> mpss on 8916?
>> To provide a history.
>> We got a internal request, where during subsystem crash/restart, in our
>> recovery path, we try to get the cause of crash by reading shared memory
>> region.
>> But, because in recovery path we write null to first character of shared
>> memory string. So, any other client which in the meantime try to dump the
>> crash region will miss first character of crash region.
>> For example: actual "err_crash_reason " will be read by other interested
>> clients as "rr_crash_reason"
>>
>> Now as this piece of code is present since long 3.10,3.18,4.4 time, so we
>> were not sure of this snippet's reason of existence. Here, initially we
>> tried to find out reason for this null write, where we guessed this snippet
>> is lying there to ensure, that across subsequent crashes, we always get a
>> new updated reason/string(as we are writing null to first character of
>> shared mem) and not some older stale string.
>>
>> But this understanding was rejected by subsystem owners saying that crash
>> reason, shared memory item is re-initialized at non-HLOS bootup so it will
>> get clear automatically.Hence, there is no need to write null character.
>>
>> So, because of above reason, we could say that this snippet is causing a bug
>> and should be fixed and this change should be valid for any platform.
> Thanks for investigating this and letting me know.
>
> As you say the only time this had the potential to be a problem would be
> if we have a fatal error with a message followed by a crash that doesn't
> fill out the message - in this case we could have read the old message.
>
> I have merged your "v1" patch - which as it's the second version of the
> patch, should be titled v2.
Thanks Bjorn.
I have termed it v1 assuming earlier patch is v0. Anyways I should have 
send out first patch
with proper version to avoid confusion.
>
> Regards,
> Bjorn
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> the body of a message to majordomo@vger.kernel.org
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Re: [PATCH] remoteproc: Remove null character write of shared mem

[Jitendra Sharma]

Hi Bjorn,


On 2/13/2018 12:42 PM, Jitendra Sharma wrote:
>
>
> On 2/13/2018 12:09 AM, Bjorn Andersson wrote:
>> On Thu 08 Feb 01:12 PST 2018, Jitendra Sharma wrote:
>>
>>> Hi Bjorn,
>>>
>>>
>>> On 2/7/2018 8:57 PM, Bjorn Andersson wrote:
>>>> On Wed 07 Feb 05:22 PST 2018, Jitendra Sharma wrote:
>>>>
>>>>> remoteproc is writing '\0' in the shared mem region. This
>>>>> region is shared among multiple clients that are also trying
>>>>> to read. Hence they miss first character.
>>>>>
>>>>> Remove this null character write, as this mem area is
>>>>> supposed to be Read only.
>>>>>
>>>>> Further during every subsystem reboot, this region is
>>>>> initialized with default, hence no need to write this
>>>>> region.
>>>> Thanks for your patch Jitendra!
>>>>
>>>> The write was removed from the downstream kernel in msm-4.9, late last
>>>> year. Can you please confirm that you describe here is valid for
>>>> platforms supported prior to this change as well?
>>>>
>>>> E.g. is what you're describing true for wcnss on 8064, adsp on 8974 
>>>> and
>>>> mpss on 8916?
>>> To provide a history.
>>> We got a internal request, where during subsystem crash/restart, in our
>>> recovery path, we try to get the cause of crash by reading shared 
>>> memory
>>> region.
>>> But, because in recovery path we write null to first character of 
>>> shared
>>> memory string. So, any other client which in the meantime try to 
>>> dump the
>>> crash region will miss first character of crash region.
>>> For example: actual "err_crash_reason " will be read by other 
>>> interested
>>> clients as "rr_crash_reason"
>>>
>>> Now as this piece of code is present since long 3.10,3.18,4.4 time, 
>>> so we
>>> were not sure of this snippet's reason of existence. Here, initially we
>>> tried to find out reason for this null write, where we guessed this 
>>> snippet
>>> is lying there to ensure, that across subsequent crashes, we always 
>>> get a
>>> new updated reason/string(as we are writing null to first character of
>>> shared mem) and not some older stale string.
>>>
>>> But this understanding was rejected by subsystem owners saying that 
>>> crash
>>> reason, shared memory item is re-initialized at non-HLOS bootup so 
>>> it will
>>> get clear automatically.Hence, there is no need to write null 
>>> character.
>>>
>>> So, because of above reason, we could say that this snippet is 
>>> causing a bug
>>> and should be fixed and this change should be valid for any platform.
>> Thanks for investigating this and letting me know.
>>
>> As you say the only time this had the potential to be a problem would be
>> if we have a fatal error with a message followed by a crash that doesn't
>> fill out the message - in this case we could have read the old message.
>>
>> I have merged your "v1" patch - which as it's the second version of the
>> patch, should be titled v2.
> Thanks Bjorn.
> I have termed it v1 assuming earlier patch is v0. Anyways I should 
> have send out first patch
> with proper version to avoid confusion.
I guess you agreed for this patch and picked in your tree. But, I am 
wondering why its still not merged in kernel mainline.
Is anything pending/missing from my side to move it further or are there 
any queries related to that patch?

Thanks,
Jitendra
>>
>> Regards,
>> Bjorn
>> -- 
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>> linux-arm-msm" in
>> the body of a message to majordomo@vger.kernel.org
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>
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