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Message-ID: <20130716192200.GA21716@redhat.com>
Date: Tue, 16 Jul 2013 21:22:00 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
Jiri Olsa <jolsa@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between
opening probe event files and deleting probe
On 07/16, Steven Rostedt wrote:
>
> On Tue, 2013-07-16 at 18:38 +0200, Oleg Nesterov wrote:
> > On 07/15, Oleg Nesterov wrote:
> > >
> > > So. As Masami pointed out, this is not enough. Probably we can add more
> > > hacks, but I'd like to discuss the alternative approach.
> > >
> > > Note also that this ref count has the unfortunate property, if someone
> > > keeps the file opened we can't remove an event.
> >
> > And please correct me, but afaics there are similar problems with
> > rmdir instances/xxx.
>
> The instances have their own refcount. And if a file is open, it wont
> remove the directory. Just try it...
I guess you mean "if (tr->ref)" check.
But tracing_open_generic_file()->trace_array_get() is racy, no?
Somehow we need to ensure it is safe to use file / file->tr.
> > > Question: why event_enable_write() needs trace_array_get() ?
> >
> > probably it doesn't...
>
> I'm confused. Which code has event_enable_write doing a
> trace_array_get()?
I meant tracing_open_generic_file(), sorry. I _think_ it can die,
please see RFC I sent.
But let me repeat once again, I do not pretend I understand this
code ;)
> I need to sort these patches out. They are all over the place. What
> exactly do we have for a solution here. Did we figure out which patches
> are needed?
Well, see above. But I think:
1. We should close open/delete races
2. We still need probe_remove_event_call() which return -EBUSY
if perf_refcount || FTRACE_EVENT_FL_ENABLED
2/4 in your series but without TRACE_EVENT_FL_REF_MASK check
3. We need the changes in trace_kprobes.c (and uprobes but lets
ignore it for now). The patch from you (3/4) and another one
from Masami (Wait for disabling all running kprobe handlers).
However, I think it would be better to discuss 3. later.
Btw, Steven, what about other pending (and orthogonal changes) ?
>From Jovi, from me. I see nothing new in linux-trace.git#for-next...
Oleg.
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