linux-kernel - Re: [PATCH v5 09/10] Uprobes/sdt: Document about reference counter

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Date:   Mon, 2 Jul 2018 07:54:44 -0700
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     oleg@...hat.com, rostedt@...dmis.org, mhiramat@...nel.org,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, linux-kernel@...r.kernel.org, corbet@....net,
        linux-doc@...r.kernel.org, ananth@...ux.vnet.ibm.com,
        alexis.berlemont@...il.com, naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com
Subject: Re: [PATCH v5 09/10] Uprobes/sdt: Document about reference counter

* 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?

Hence I would think twice of advertising this mechanism. i.e keep this
as an undocumented feature.