From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Brian Gerst <brgerst@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
Thomas Gleixner <tglx@linutronix.de>,
Denys Vlasenko <dvlasenk@redhat.com>,
Ingo Molnar <mingo@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Borislav Petkov <bp@suse.de>, "H. Peter Anvin" <hpa@zytor.com>,
X86 ML <x86@kernel.org>
Subject: Re: [PATCH 3/4] x86: Rewrite switch_to() code
Date: Mon, 23 May 2016 07:05:34 -0500 [thread overview]
Message-ID: <20160523120534.lzphuumzemvrmuwg@treble> (raw)
In-Reply-To: <CAMzpN2jbnCAN_xZbwdBziOEq_xebApNWyBN_vJ2s9z9RnXA7gg@mail.gmail.com>
On Mon, May 23, 2016 at 07:49:37AM -0400, Brian Gerst wrote:
> On Mon, May 23, 2016 at 7:40 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > On Sun, May 22, 2016 at 09:47:22PM -0700, Andy Lutomirski wrote:
> >> On Sun, May 22, 2016 at 7:34 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >> > On Sun, May 22, 2016 at 10:59:38AM -0700, Andy Lutomirski wrote:
> >> >> cc: Josh Poimboeuf: do you care about the exact stack layout of the
> >> >> bottom of the stack of an inactive task?
> >> >
> >> > So there's one minor issue with this patch, relating to unwinding the
> >> > stack of a newly forked task. For detecting reliable stacks, the
> >> > unwinder needs to unwind all the way to the syscall pt_regs to make sure
> >> > the stack is sane. But for newly forked tasks, that won't be possible
> >> > here because the unwinding will stop at the fork_frame instead.
> >> >
> >> > So from an unwinder standpoint it might be nice for copy_thread_tls() to
> >> > place a frame pointer on the stack next to the ret_from_fork return
> >> > address, so that it would resemble an actual stack frame. The frame
> >> > pointer could probably just be hard-coded to zero. And then the first
> >> > bp in fork_frame would need to be a pointer to it instead of zero. That
> >> > would make it nicely resemble the stack of any other task.
> >> >
> >> > Alternatively I could teach the unwinder that if the unwinding starts at
> >> > the fork_frame offset from the end of the stack page, and the saved rbp
> >> > is zero, it can assume that it's a newly forked task. But that seems a
> >> > little more brittle to me, as it requires the unwinder to understand
> >> > more of the internal workings of the fork code.
> >> >
> >> > But overall I think this patch is a really nice cleanup, and other than
> >> > the above minor issue it should be fine with my reliable unwinder, since
> >> > rbp is still at the top of the stack.
> >>
> >> Is this a regression or is there some reason that it works right
> >> without the patch?
> >
> > Without the patch, it uses TIF_FORK to determine the stack is empty.
>
> Where is this code? I don't see it in the mainline kernel.
Yeah, it hasn't been merged. Here's the last version:
https://lkml.kernel.org/r/4d34d452bf8f85c7d6d5f93db1d3eeb4cba335c7.1461875890.git.jpoimboe@redhat.com
--
Josh
next prev parent reply other threads:[~2016-05-23 12:05 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-21 16:04 [PATCH 0/4] x86: Rewrite switch_to() Brian Gerst
2016-05-21 16:04 ` [PATCH 1/4] x86: Save return value from kernel_thread Brian Gerst
2016-05-22 1:44 ` Andy Lutomirski
2016-05-22 2:19 ` Brian Gerst
2016-05-21 16:04 ` [PATCH 2/4] x86-32, kgdb: Don't use thread.ip in sleeping_thread_to_gdb_regs() Brian Gerst
2016-05-23 17:05 ` Andy Lutomirski
2016-05-21 16:04 ` [PATCH 3/4] x86: Rewrite switch_to() code Brian Gerst
2016-05-22 17:59 ` Andy Lutomirski
2016-05-22 19:31 ` Brian Gerst
2016-05-22 21:07 ` Andy Lutomirski
2016-05-23 2:34 ` Josh Poimboeuf
2016-05-23 4:47 ` Andy Lutomirski
2016-05-23 11:40 ` Josh Poimboeuf
2016-05-23 11:49 ` Brian Gerst
2016-05-23 12:05 ` Josh Poimboeuf [this message]
2016-05-23 11:14 ` Brian Gerst
2016-05-23 11:47 ` Josh Poimboeuf
2016-05-23 11:49 ` Josh Poimboeuf
2016-05-23 16:46 ` Josh Poimboeuf
2016-05-23 17:03 ` Andy Lutomirski
2016-05-23 18:44 ` Josh Poimboeuf
2016-07-12 14:16 ` Josh Poimboeuf
2016-06-15 1:31 ` Andy Lutomirski
2016-06-15 8:03 ` Ingo Molnar
2016-06-15 11:52 ` Brian Gerst
2016-05-21 16:04 ` [PATCH 4/4] x86: Pass kernel thread parameters in fork_frame Brian Gerst
2016-05-22 18:01 ` Andy Lutomirski
2016-05-22 19:21 ` Brian Gerst
2016-05-23 15:23 ` Josh Poimboeuf
2016-05-23 15:36 ` Andy Lutomirski
2016-05-23 21:04 ` Brian Gerst
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