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Message-Id: <0110cd8a-9785-c761-e2a5-ba8ab92745e9@linux.ibm.com>
Date: Tue, 3 Jul 2018 13:20:29 +0530
From: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc: oleg@...hat.com, rostedt@...dmis.org, mhiramat@...nel.org,
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Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v5 09/10] Uprobes/sdt: Document about reference counter
Hi Srikar,
On 07/02/2018 08:24 PM, Srikar Dronamraju wrote:
> * Ravi Bangoria <ravi.bangoria@...ux.ibm.com> [2018-06-28 10:52:08]:
>
>> Reference counter gate the invocation of probe. If present,
>> by default reference count is 0. Kernel needs to increment
>> it before tracing the probe and decrement it when done. This
>> is identical to semaphore in Userspace Statically Defined
>> Tracepoints (USDT).
>>
>> Document usage of reference counter.
>>
>> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
>> Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
>
> Unlike perf, this mechanism cannot detect ref count and depends on the
> users data. What happens if the user mistakenly provides a wrong location?
> I guess he can corrupt some other data structures?
Yes, if user is giving wrong ref_ctr_offset, uprobe infrastructure will
corrupt some user data.
>
> Hence I would think twice of advertising this mechanism. i.e keep this
> as an undocumented feature.
>
I don't mind.
Thanks,
Ravi
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