From: Masami Hiramatsu <mhiramat@redhat.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
lkml <linux-kernel@vger.kernel.org>,
systemtap <systemtap@sources.redhat.com>,
DLE <dle-develop@lists.sourceforge.net>,
Jim Keniston <jkenisto@us.ibm.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Christoph Hellwig <hch@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Anders Kaseorg <andersk@ksplice.com>,
Tim Abbott <tabbott@ksplice.com>,
Andi Kleen <andi@firstfloor.org>,
Jason Baron <jbaron@redhat.com>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Subject: Re: [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump optimization
Date: Tue, 24 Nov 2009 20:59:00 -0000 [thread overview]
Message-ID: <4B0C492D.1060602@redhat.com> (raw)
In-Reply-To: <20091124201357.GB5071@nowhere>
Frederic Weisbecker wrote:
> On Tue, Nov 24, 2009 at 10:34:16AM -0500, Masami Hiramatsu wrote:
>> Frederic Weisbecker wrote:
>>> I _might_ have understood.
>>> You have set up the optimized flags, then you wait for
>>> any old-style int 3 kprobes to complete and route
>>> to detour buffer so that you can patch the jump
>>> safely in the dead code? (and finish with first byte
>>> by patching the int 3 itself)
>>>
>>
>> Yeah, you might get almost correct answer.
>> The reason why we have to wait scheduling on all processors
>> is that this code may modify N instructions (not a single
>> instruction). This means, there is a chance that 2nd to nth
>> instructions are interrupted on other cpus when we start
>> code modifying.
>
>
> Aaah ok!
>
> In this case, you probably just need the synchronize_sched()
> thing. The delayed work looks unnecessary.
Yeah, the delayed work is for speeding up batch registration
which kprobes are already supported. Sometimes ~100 probes
can be set via batch registration I/F.
>> Please imagine that 2nd instruction is interrupted and
>> stop_machine() replaces the 2nd instruction with jump
>> *address* while running interrupt handler. When the interrupt
>> returns to original address, there is no valid instructions
>> and it causes unexpected result.
>
>
> Yeah.
>
>
>>
>> To avoid this situation, we have to wait a scheduler quiescent
>> state on all cpus, because it also ensure that all current
>> interruption are done.
>
>
> Ok.
>
>
>> This also excuses why we don't need to wait when unoptimizing
>> and why it has not supported preemptive kernel yet.
>
>
> I see...so the non-preemptible kernel requirement looks
> hard to workaround :-s
It's the next challenge I think :-)
Even though, kprobes itself still work on preemptive kernel,
so we don't lose any functionality.
>> In unoptimizing case, since there is just a single instruction
>> (jump), there is no nth instruction which can be interrupted.
>> Thus we can just use a stop_machine(). :-)
>
>
> Ok.
>
>
>>
>> On the preemptive kernel, waiting scheduling is not work as we
>> see on non-preemptive kernel. Since processes can be preempted
>> in interruption, we can't ensure that the current running
>> interruption is done. (I assume that a pair of freeze_processes
>> and thaw_processes may possibly ensure that, or maybe we can
>> share some stack rewinding code with ksplice.)
>> So it depends on !PREEMPT.
>
>
>
> Right.
> However using freeze_processes() and thaw_processes() would be
> probably too costly and it's not a guarantee that every processes
> go to the refrigerator() :-), because some tasks are not freezable,
> like the kernel threads by default if I remember well, unless they
> call set_freezable(). That's a pity, we would just have needed
> to set __kprobe in refrigerator().
Ah, right. Even though, we still have an option of ksplice code.
Thank you,
> PS: hmm btw I remember about a patch that
> tagged refrigerator() as __cold but it looks like it hasn't been
> applied....
>
> Thanks.
>
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com
next prev parent reply other threads:[~2009-11-24 20:59 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-11-23 23:18 [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support Masami Hiramatsu
2009-11-23 23:18 ` [PATCH -tip v5 02/10] kprobes: Introduce generic insn_slot framework Masami Hiramatsu
2009-11-23 23:18 ` [PATCH -tip v5 01/10] kprobes/x86: Cleanup RELATIVEJUMP_INSTRUCTION to RELATIVEJUMP_OPCODE Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 03/10] kprobes: Introduce kprobes jump optimization Masami Hiramatsu
2009-11-24 2:44 ` Frederic Weisbecker
2009-11-24 3:31 ` Frederic Weisbecker
2009-11-24 15:32 ` Masami Hiramatsu
2009-11-24 20:14 ` Frederic Weisbecker
2009-11-24 20:59 ` Masami Hiramatsu [this message]
2009-11-25 21:09 ` Steven Rostedt
2009-11-25 21:30 ` Masami Hiramatsu
2009-11-24 21:12 ` H. Peter Anvin
2009-11-24 15:31 ` Masami Hiramatsu
2009-11-24 19:45 ` Frederic Weisbecker
2009-11-24 21:15 ` Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 05/10] kprobes/x86: Boost probes when reentering Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 07/10] kprobes/x86: Support kprobes jump optimization on x86 Masami Hiramatsu
2009-11-24 3:15 ` Frederic Weisbecker
2009-11-24 16:27 ` Jason Baron
2009-11-24 17:46 ` Masami Hiramatsu
2009-11-25 16:12 ` Masami Hiramatsu
2009-11-24 16:42 ` H. Peter Anvin
2009-11-24 17:01 ` Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 04/10] kprobes: Jump optimization sysctl interface Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 06/10] kprobes/x86: Cleanup save/restore registers Masami Hiramatsu
2009-11-24 2:51 ` Frederic Weisbecker
2009-11-24 15:36 ` Masami Hiramatsu
2009-11-24 20:19 ` Frederic Weisbecker
2009-11-24 15:40 ` Frank Ch. Eigler
2009-11-24 20:20 ` Frederic Weisbecker
2009-11-23 23:19 ` [PATCH -tip v5 10/10] [RFC] kprobes/x86: Use text_poke_fixup() for jump optimization Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 09/10] [RFC] x86: Introduce generic jump patching without stop_machine Masami Hiramatsu
2009-11-23 23:19 ` [PATCH -tip v5 08/10] kprobes: Add documents of jump optimization Masami Hiramatsu
2009-11-24 2:03 ` [PATCH -tip v5 00/10] kprobes: Kprobes jump optimization support Frederic Weisbecker
2009-11-24 3:20 ` Frederic Weisbecker
2009-11-24 7:53 ` Ingo Molnar
2009-11-24 16:03 ` Masami Hiramatsu
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