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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