From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Dave Watson <davejwatson@fb.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
linux-api <linux-api@vger.kernel.org>,
Paul Turner <pjt@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Russell King <linux@arm.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andrew Hunter <ahh@google.com>, Andi Kleen <andi@firstfloor.org>,
Chris Lameter <cl@linux.com>, Ben Maurer <bmaurer@fb.com>,
rostedt <rostedt@goodmis.org>,
Josh Triplett <josh@joshtriplett.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)
Date: Mon, 16 Apr 2018 11:39:48 -0700 [thread overview]
Message-ID: <CA+55aFzZtY5ELKc+TGf9BA6px300BNzedadm_yNXzODTKN=HgQ@mail.gmail.com> (raw)
In-Reply-To: <542721578.11358.1523903708510.JavaMail.zimbra@efficios.com>
On Mon, Apr 16, 2018 at 11:35 AM, Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
> Specifically for single-stepping, the __rseq_table section introduced
> at user-level will allow newer debuggers and tools which do line and
> instruction-level single-stepping to skip over rseq critical sections.
> However, this breaks existing debuggers and tools.
I really don't think single-stepping is a valid argument.
Even if the cpu_opv() allows you to "single step", you're not actually
single stepping the same thing that you're using. So you are literally
debugging something else than the real code.
At that point, you don't need "cpu_opv()", you need to just load
/dev/urandom in a buffer, and single-step that. Ta-daa! No new kernel
functionality needed.
So if the main argument for cpu_opv is single-stepping, then just rip
it out. It's not useful.
Anybody who cares deeply about single-stepping shouldn't be using
optimistic algorithms, and they shouldn't be doing multi-threaded
stuff either. They won't be able to use things like transactional
memory either.
You can't single-step into the kernel to see what the kernel does
either when you're debugging something.
News at 11: "single stepping isn't always viable".
Linus
next prev parent reply other threads:[~2018-04-16 18:39 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 19:27 [RFC PATCH for 4.18 00/23] Restartable sequences and CPU op vector Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 01/23] uapi headers: Provide types_32_64.h (v2) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 02/23] rseq: Introduce restartable sequences system call (v13) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 03/23] arm: Add restartable sequences support Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 04/23] arm: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 05/23] x86: Add support for restartable sequences (v2) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 06/23] x86: Wire up restartable sequence system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 07/23] powerpc: Add support for restartable sequences Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 08/23] powerpc: Wire up restartable sequences system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 09/23] sched: Implement push_task_to_cpu (v2) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 10/23] mm: Introduce vm_map_user_ram, vm_unmap_user_ram Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 11/23] mm: Provide is_vma_noncached Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7) Mathieu Desnoyers
2018-04-12 19:43 ` Linus Torvalds
2018-04-12 19:59 ` Mathieu Desnoyers
2018-04-12 20:07 ` Linus Torvalds
2018-04-13 12:16 ` Mathieu Desnoyers
2018-04-13 16:37 ` Linus Torvalds
2018-04-13 18:06 ` Mathieu Desnoyers
2018-04-12 20:23 ` Andi Kleen
2018-04-16 16:28 ` Mathieu Desnoyers
2018-04-16 17:02 ` Andi Kleen
2018-04-14 22:44 ` Andy Lutomirski
2018-04-16 18:35 ` Mathieu Desnoyers
2018-04-16 18:39 ` Linus Torvalds [this message]
2018-04-16 19:21 ` Mathieu Desnoyers
2018-04-16 19:26 ` Linus Torvalds
2018-04-16 20:58 ` Mathieu Desnoyers
2018-05-04 14:32 ` Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 13/23] x86: Wire up cpu_opv system call Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 14/23] powerpc: " Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 15/23] arm: " Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 16/23] selftests: lib.mk: Introduce OVERRIDE_TARGETS Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 17/23] cpu_opv: selftests: Implement selftests (v7) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 18/23] rseq: selftests: Provide rseq library (v5) Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 19/23] rseq: selftests: Provide percpu_op API Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 20/23] rseq: selftests: Provide basic test Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 21/23] rseq: selftests: Provide basic percpu ops test Mathieu Desnoyers
2018-04-12 19:27 ` [RFC PATCH for 4.18 22/23] rseq: selftests: Provide parametrized tests Mathieu Desnoyers
2018-04-12 19:28 ` [RFC PATCH for 4.18 23/23] rseq: selftests: Provide Makefile, scripts, gitignore Mathieu Desnoyers
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