linux-kernel - Re: [PATCH v5 06/10] Uprobes: Support SDT markers having reference count (semaphore)

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Message-Id: <a37cc94b-5940-643c-3e81-fc375c6aada0@linux.ibm.com>
Date:   Mon, 16 Jul 2018 13:50:10 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     Oleg Nesterov <oleg@...hat.com>, srikar@...ux.vnet.ibm.com,
        rostedt@...dmis.org, mhiramat@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org,
        open list <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,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v5 06/10] Uprobes: Support SDT markers having reference
 count (semaphore)

Hi Song,

On 07/14/2018 05:20 AM, Song Liu wrote:
> 
> Hmm... what happens when we have multiple uprobes sharing the same
> reference counter? It feels equally complicate to me. Or did I miss any
> cases here?


As far as I can think of, it should be handled by default. No special
treatment needed for this.

...

> 
> This patch tries to resolve this imbalance by passing extra flag
> "restore_insn" to probe_event_disable().
> 
> Signed-off-by: Song Liu <songliubraving@...com>


Ah cool. Seems this will make them balanced. But is it fine to change
uprobe_unregister()? It's already an ABI. No other way around?

Also, one more source of imbalance is this condition:

          if (is_register)
                  flags |= VM_WRITE;

in valid_vma(). You need to take care of that as well.

Thanks,
Ravi