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From: "Björn Töpel" <bjorn@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Guo Ren <guoren@kernel.org>,
	"liaochang (A)" <liaochang1@huawei.com>,
	palmer@dabbelt.com, paul.walmsley@sifive.com,
	mhiramat@kernel.org, conor.dooley@microchip.com,
	penberg@kernel.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH] riscv: kprobe: Optimize kprobe with accurate atomicity
Date: Mon, 30 Jan 2023 17:56:43 +0100	[thread overview]
Message-ID: <87edrc2c6s.fsf@all.your.base.are.belong.to.us> (raw)
In-Reply-To: <Y9fm+6LPXgtDSma/@FVFF77S0Q05N>

Mark Rutland <mark.rutland@arm.com> writes:

>> ...and stop_machine() with !PREEMPTION is broken as well, when you're
>> replacing multiple instructions (see Mark's post at [1]). The
>> stop_machine() dance might work when you're replacing *one* instruction,
>> not multiple as in the RISC-V case. I'll expand on this in a comment in
>> the OPTPROBES v6 series.
>
> Just to clarify, my comments in [1] were assuming that stop_machine() was not
> used, in which case there is a problem with or without PREEMPTION.
>
> I believe that when using stop_machine(), the !PREEMPTION case is fine, since
> stop_machine() schedules work rather than running work in IRQ context on the
> back of an IPI, so no CPUs should be mid-sequnce during the patching, and it's
> not possible for there to be threads which are preempted mid-sequence.

TIL! stop_cpus() highlights that very nicely. Thanks for clearing that
out! That's good news; That means that this fix [4] should go in.

> That all said, IIUC optprobes is going to disappear once fprobe is ready
> everywhere, so that might be moot.

Yes (However, the stop_machine()/!PREEMPTION issue was with ftrace).


Björn

[4] https://lore.kernel.org/lkml/20230107133549.4192639-2-guoren@kernel.org/

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WARNING: multiple messages have this Message-ID (diff)
From: "Björn Töpel" <bjorn@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Guo Ren <guoren@kernel.org>,
	"liaochang (A)" <liaochang1@huawei.com>,
	palmer@dabbelt.com, paul.walmsley@sifive.com,
	mhiramat@kernel.org, conor.dooley@microchip.com,
	penberg@kernel.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH] riscv: kprobe: Optimize kprobe with accurate atomicity
Date: Mon, 30 Jan 2023 17:56:43 +0100	[thread overview]
Message-ID: <87edrc2c6s.fsf@all.your.base.are.belong.to.us> (raw)
In-Reply-To: <Y9fm+6LPXgtDSma/@FVFF77S0Q05N>

Mark Rutland <mark.rutland@arm.com> writes:

>> ...and stop_machine() with !PREEMPTION is broken as well, when you're
>> replacing multiple instructions (see Mark's post at [1]). The
>> stop_machine() dance might work when you're replacing *one* instruction,
>> not multiple as in the RISC-V case. I'll expand on this in a comment in
>> the OPTPROBES v6 series.
>
> Just to clarify, my comments in [1] were assuming that stop_machine() was not
> used, in which case there is a problem with or without PREEMPTION.
>
> I believe that when using stop_machine(), the !PREEMPTION case is fine, since
> stop_machine() schedules work rather than running work in IRQ context on the
> back of an IPI, so no CPUs should be mid-sequnce during the patching, and it's
> not possible for there to be threads which are preempted mid-sequence.

TIL! stop_cpus() highlights that very nicely. Thanks for clearing that
out! That's good news; That means that this fix [4] should go in.

> That all said, IIUC optprobes is going to disappear once fprobe is ready
> everywhere, so that might be moot.

Yes (However, the stop_machine()/!PREEMPTION issue was with ftrace).


Björn

[4] https://lore.kernel.org/lkml/20230107133549.4192639-2-guoren@kernel.org/

  reply	other threads:[~2023-01-30 16:58 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-26 16:15 [PATCH] riscv: kprobe: Optimize kprobe with accurate atomicity guoren
2023-01-26 16:15 ` guoren
2023-01-28  3:52 ` liaochang (A)
2023-01-28  3:52   ` liaochang (A)
2023-01-28  4:45   ` Guo Ren
2023-01-28  4:45     ` Guo Ren
2023-01-30 15:28     ` Björn Töpel
2023-01-30 15:28       ` Björn Töpel
2023-01-30 15:49       ` Mark Rutland
2023-01-30 15:49         ` Mark Rutland
2023-01-30 16:56         ` Björn Töpel [this message]
2023-01-30 16:56           ` Björn Töpel
2023-01-31  1:48         ` Guo Ren
2023-01-31  1:48           ` Guo Ren
2023-01-31  7:12           ` Björn Töpel
2023-01-31  7:12             ` Björn Töpel
2023-01-31  8:30             ` Guo Ren
2023-01-31  8:30               ` Guo Ren
2023-01-31 10:33           ` Mark Rutland
2023-01-31 10:33             ` Mark Rutland
2023-02-16 15:23             ` Masami Hiramatsu
2023-02-16 15:23               ` Masami Hiramatsu
2023-02-20 10:35               ` Mark Rutland
2023-02-20 10:35                 ` Mark Rutland
2023-02-21  1:30               ` Guo Ren
2023-02-21  1:30                 ` Guo Ren
2023-01-31  1:01       ` Guo Ren
2023-01-31  1:01         ` Guo Ren
2023-01-31  1:09         ` Guo Ren
2023-01-31  1:09           ` Guo Ren
2023-01-31  7:03           ` Björn Töpel
2023-01-31  7:03             ` Björn Töpel
2023-01-31  8:27             ` Guo Ren
2023-01-31  8:27               ` Guo Ren
2023-01-31  6:40         ` Björn Töpel
2023-01-31  6:40           ` Björn Töpel
2023-01-31  8:15           ` Guo Ren
2023-01-31  8:15             ` Guo Ren
2023-01-31 10:56             ` Andrea Parri
2023-01-31 10:56               ` Andrea Parri
2023-01-31 13:23               ` Guo Ren
2023-01-31 13:23                 ` Guo Ren
2023-02-16  7:54                 ` Björn Töpel
2023-02-16  7:54                   ` Björn Töpel
2023-02-17  2:28                   ` Guo Ren
2023-02-17  2:28                     ` Guo Ren
2023-02-17  7:32                     ` Björn Töpel
2023-02-17  7:32                       ` Björn Töpel
2023-02-21  1:56                       ` Guo Ren
2023-02-21  1:56                         ` Guo Ren
2023-02-16 15:42 ` Masami Hiramatsu
2023-02-16 15:42   ` Masami Hiramatsu
2023-02-21  0:57   ` Guo Ren
2023-02-21  0:57     ` Guo Ren

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