Messages in this thread | | | Date | Tue, 16 Jul 2013 21:22:00 +0200 | From | Oleg Nesterov <> | Subject | Re: [RFC][PATCH 0/4] tracing/kprobes/uprobes: Fix race between opening probe event files and deleting probe |
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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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