linux-kernel - Re: [PATCH 1/4] ftrace: Fix function pid filter on instances

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170328225843.4ed16b0f@grimm.local.home>
Date:   Tue, 28 Mar 2017 22:58:43 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, kernel-team@....com
Subject: Re: [PATCH 1/4] ftrace: Fix function pid filter on instances

On Wed, 29 Mar 2017 11:42:27 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> On Tue, Mar 28, 2017 at 10:28:55PM -0400, Steven Rostedt wrote:
> > On Wed, 29 Mar 2017 11:20:37 +0900
> > Namhyung Kim <namhyung@...nel.org> wrote:
> > 
> >   
> > > > Actually, if this is called after event_trace_del_tracer(), the tr is
> > > > already invisible and nothing new should change.    
> > > 
> > > I don't follow.  After event_trace_del_tracer(), the tr is invisible
> > > from the probe of event tracing but still is visible from the probe of
> > > function tracing, right?  
> > 
> > Well, nothing should be able to get to the set_ftrace_filter file when
> > there. Because of the tr->ref count. But keeping the lock is safer
> > regardless, and it's not a fast path, so the extra overhead if the lock
> > isn't needed is no big deal.  
> 
> Oh, I meant if a pid filter was already set when removing the
> instance.  Function filters should be inactive since function tracer
> was finished (via tracing_set_nop), but the probe on sched_switch
> event (for pid filter) is still active and references the tr.
> 

I think we are talking about two different things. I was simply talking
about the need to take the ftrace_lock or not in the
clear_ftrace_pids() call here. I don't think we have to, because nothing
should be in contention with it at that point. But it doesn't hurt to
take it.

-- Steve