Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking
Date	2016-04-30 02:10 +0200
Message-ID	<rtqDU-6Oh-5@gated-at.bofh.it> (permalink)
References	(5 earlier) <rtnd0-3HL-37@gated-at.bofh.it> <rtnmG-3LT-21@gated-at.bofh.it> <rto93-4rM-5@gated-at.bofh.it> <rtoiK-4yd-23@gated-at.bofh.it> <rtpot-5CD-1@gated-at.bofh.it>
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On Apr 29, 2016 3:41 PM, "Josh Poimboeuf" <jpoimboe@redhat.com> wrote:
>
> On Fri, Apr 29, 2016 at 02:37:41PM -0700, Andy Lutomirski wrote:
> > On Fri, Apr 29, 2016 at 2:25 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > > I think the easiest way to make it work would be to modify the idtentry
> > > macro to put all the idt entries in a dedicated section.  Then the
> > > unwinder could easily detect any calls from that code.
> >
> > That would work.  Would it make sense to do the same for the irq entries?
>
> Yes, I think so.
>
> > >> I suppose we could try to rejigger the code so that rbp points to
> > >> pt_regs or similar.
> > >
> > > I think we should avoid doing something like that because it would break
> > > gdb and all the other unwinders who don't know about it.
> >
> > How so?
> >
> > Currently, rbp in the entry code is meaningless.  I'm suggesting that,
> > when we do, for example, 'call \do_sym' in idtentry, we point rbp to
> > the pt_regs.  Currently it points to something stale (which the
> > dump_stack code might be relying on.  Hmm.)  But it's probably also
> > safe to assume that if you unwind to the 'call \do_sym', then pt_regs
> > is the next thing on the stack, so just doing the section thing would
> > work.
>
> Yes, rbp is meaningless on the entry from user space.  But if an
> in-kernel interrupt occurs (e.g. page fault, preemption) and you have
> nested entry, rbp keeps its old value, right?  So the unwinder can walk
> past the nested entry frame and keep going until it gets to the original
> entry.

Yes.

It would be nice if we could do better, though, and actually notice
the pt_regs and identify the entry.  For example, I'd love to see
"page fault, RIP=xyz" printed in the middle of a stack dump on a
crash.  Also, I think that just following rbp links will lose the
actual function that took the page fault (or whatever function
pt_regs->ip actually points to).

>
> > We should really re-add DWARF some day.
>
> Working on it :-)

Excellent.

Have you looked at my vdso unwinding test at all?  If we could do
something similar for the kernel, IMO it would make testing much more
pleasant.

--Andy

Thread

[RFC PATCH v2 00/18] livepatch: hybrid consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
  [RFC PATCH v2 14/18] livepatch: remove unnecessary object loaded check Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
  [RFC PATCH v2 10/18] livepatch/powerpc: add TIF_PATCH_PENDING thread flag Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
    Re: [RFC PATCH v2 10/18] livepatch/powerpc: add TIF_PATCH_PENDING  thread flag Petr Mladek <pmladek@suse.com> - 2016-05-03 11:10 +0200
      Re: [RFC PATCH v2 10/18] livepatch/powerpc: add TIF_PATCH_PENDING  thread flag Miroslav Benes <mbenes@suse.cz> - 2016-05-03 14:10 +0200
  [RFC PATCH v2 16/18] livepatch: store function sizes Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
  [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
    Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-04-29 20:10 +0200
      Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-04-29 22:20 +0200
        Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 22:30 +0200
          Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-04-29 22:40 +0200
            Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 23:30 +0200
              Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-04-29 23:40 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Jiri Kosina <jikos@kernel.org> - 2016-04-30 00:20 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-30 01:00 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-04-30 02:20 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-30 00:50 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-04-30 02:10 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-02 16:00 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-05-02 18:00 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-02 19:40 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-05-02 20:20 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Ingo Molnar <mingo@kernel.org> - 2016-05-02 20:40 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-02 21:50 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Jiri Kosina <jikos@kernel.org> - 2016-05-02 22:00 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Jiri Kosina <jikos@kernel.org> - 2016-05-02 22:10 +0200
                Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking Andy Lutomirski <luto@amacapital.net> - 2016-05-03 02:50 +0200
                RE: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking David Laight <David.Laight@ACULAB.COM> - 2016-05-04 17:20 +0200
      Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ  tracking Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 22:20 +0200
  [RFC PATCH v2 09/18] livepatch/x86: add TIF_PATCH_PENDING thread flag Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
    Re: [RFC PATCH v2 09/18] livepatch/x86: add TIF_PATCH_PENDING thread flag Andy Lutomirski <luto@amacapital.net> - 2016-04-29 20:10 +0200
      Re: [RFC PATCH v2 09/18] livepatch/x86: add TIF_PATCH_PENDING thread  flag Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 22:20 +0200
  [RFC PATCH v2 02/18] x86/asm/head: use a common function for starting CPUs Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
  [RFC PATCH v2 13/18] livepatch: separate enabled and patched states Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
    Re: [RFC PATCH v2 13/18] livepatch: separate enabled and patched  states Petr Mladek <pmladek@suse.com> - 2016-05-03 11:40 +0200
      Re: [RFC PATCH v2 13/18] livepatch: separate enabled and patched  states Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-03 15:50 +0200
  [RFC PATCH v2 06/18] x86: dump_trace() error handling Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 22:50 +0200
    Re: [RFC PATCH v2 06/18] x86: dump_trace() error handling Minfei Huang <mnghuan@gmail.com> - 2016-04-29 15:50 +0200
      Re: [RFC PATCH v2 06/18] x86: dump_trace() error handling Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 16:10 +0200
  [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the stack for idle tasks Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 23:00 +0200
    Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Brian Gerst <brgerst@gmail.com> - 2016-04-29 20:50 +0200
      Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 22:30 +0200
    Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Andy Lutomirski <luto@kernel.org> - 2016-04-29 21:40 +0200
      Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-29 23:00 +0200
        Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Andy Lutomirski <luto@amacapital.net> - 2016-04-29 23:40 +0200
          Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-30 01:30 +0200
            Re: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the  stack for idle tasks Andy Lutomirski <luto@amacapital.net> - 2016-04-30 02:20 +0200
  [RFC PATCH v2 04/18] x86: move _stext marker before head code Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 23:00 +0200
  [RFC PATCH v2 01/18] x86/asm/head: clean up initial stack variable Josh Poimboeuf <jpoimboe@redhat.com> - 2016-04-28 23:00 +0200
  Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Petr Mladek <pmladek@suse.com> - 2016-05-04 10:50 +0200
    Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-04 18:00 +0200
      Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Miroslav Benes <mbenes@suse.cz> - 2016-05-05 11:50 +0200
      Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Petr Mladek <pmladek@suse.com> - 2016-05-05 15:10 +0200
  barriers: was: [RFC PATCH v2 17/18] livepatch: change to a per-task  consistency model Petr Mladek <pmladek@suse.com> - 2016-05-04 14:40 +0200
    Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Peter Zijlstra <peterz@infradead.org> - 2016-05-04 16:00 +0200
      Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-04 19:00 +0200
    Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Petr Mladek <pmladek@suse.com> - 2016-05-04 16:20 +0200
      Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-04 19:30 +0200
        Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Petr Mladek <pmladek@suse.com> - 2016-05-05 13:30 +0200
        Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Miroslav Benes <mbenes@suse.cz> - 2016-05-09 17:50 +0200
    Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-04 19:10 +0200
      Re: barriers: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Petr Mladek <pmladek@suse.com> - 2016-05-05 12:30 +0200
  klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Petr Mladek <pmladek@suse.com> - 2016-05-04 16:50 +0200
    Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to  a per-task consistency model Jiri Kosina <jikos@kernel.org> - 2016-05-04 17:00 +0200
    Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-04 20:00 +0200
      Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Petr Mladek <pmladek@suse.com> - 2016-05-05 14:00 +0200
        Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-06 14:40 +0200
          Re: klp_task_patch: was: [RFC PATCH v2 17/18] livepatch: change to a  per-task consistency model Petr Mladek <pmladek@suse.com> - 2016-05-09 14:30 +0200
  Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Petr Mladek <pmladek@suse.com> - 2016-05-06 13:40 +0200
    Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-06 14:50 +0200
  Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Miroslav Benes <mbenes@suse.cz> - 2016-05-09 11:50 +0200
  Re: [RFC PATCH v2 17/18] livepatch: change to a per-task consistency  model Miroslav Benes <mbenes@suse.cz> - 2016-05-10 13:50 +0200

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