linux-kernel - Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore)

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Date:   Mon, 13 Aug 2018 13:08:34 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     srikar@...ux.vnet.ibm.com, Oleg Nesterov <oleg@...hat.com>,
        Steven Rostedt <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>,
        ananth@...ux.vnet.ibm.com,
        Alexis Berlemont <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 v8 3/6] Uprobes: Support SDT markers having reference
 count (semaphore)

Hi Song,

On 08/13/2018 11:17 AM, Ravi Bangoria wrote:
>>> +
>>> +static void delayed_uprobe_remove(struct uprobe *uprobe, struct mm_struct *mm)
>>> +{
>>> +       struct list_head *pos, *q;
>>> +       struct delayed_uprobe *du;
>>> +
>>> +       if (!uprobe && !mm)
>>> +               return;
>> And do we really need this check?
> 
> 
> Yes. delayed_uprobe_remove(uprobe=NULL, mm=NULL) is an invalid case. If I remove
> this check, code below (or more accurately code suggested by Oleg) will remove
> all entries from delayed_uprobe_list. So I will keep this check but put a comment
> above function.
> 

Sorry, my bad. Please ignore above comment. Even though, it saves us
to unnecessary loop over entire delayed_uprobe_list when both uprobe
and mm are NULL, that case is not possible with current code. Also,
I'm not dereferencing any of them. So, IMHO it's fine to remove this
check.

Thanks,
Ravi