Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code

From	Josh Poimboeuf <jpoimboe@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code
Date	2016-07-23 15:00 +0200
Message-ID	<rY4H7-2Tb-11@gated-at.bofh.it> (permalink)
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On Sat, Jul 23, 2016 at 02:39:52PM +0900, Linus Torvalds wrote:
> On Sat, Jul 23, 2016 at 2:35 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >
> > While doing the scanning and printing, it does call the frame pointer
> > unwinder in parallel, but like before, that's *only* used to determine
> > whether a found address should be printed without a question mark.  If
> > the unwinder goes off the rails, the scanning and printing of text
> > addresses goes on, undisturbed.
> >
> > The frame pointer unwinder code itself is quite careful not to
> > dereference anything it shouldn't (though of course I welcome any review
> > comments that find otherwise).
> 
> So this was the bug the last time around we did unwinders - the code
> would dereference the unwind tables, and the tables would be
> corrupted. End result: recursive oops.
> 
> And they were corrupted not even because of memory corruption, but
> simply because they contained incorrect data, due to compiler bugs and
> other issues.
> 
> I have really bad memories from that time. Several years after the
> fact. It took months to finally revert the crap, because the author
> continued to insist that "this was the last bug" for several passes
> through that thing.
> 
> As they say, "Once burned, twice shy". But in this case, it's more
> like "Four times burned, sixteen times as shy".

But that was DWARF, right?  This is still just simple frame pointers.

Don't think of it as a new unwinder.  Think of it instead as a "gentle
reshuffling of the existing code to vastly improve readability and
maintenance."

Yes, I would like to eventually propose a DWARF unwinder, which
hopefully learns from the mistakes of previous attempts.  But either
way, I think this patch set stands on its own as a big improvement.

-- 
Josh

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[PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 05/19] x86/dumpstack: fix function graph tracing stack dump reliability issues Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 04/19] x86/dumpstack: make printk_stack_address() more generally useful Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 18/19] x86/dumpstack: print stack identifier on its own line Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 13/19] x86/stacktrace: convert save_stack_trace_*() to the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
    Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Andy Lutomirski <luto@amacapital.net> - 2016-07-22 00:40 +0200
      Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-22 05:40 +0200
        Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Andy Lutomirski <luto@amacapital.net> - 2016-07-22 07:20 +0200
          Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-22 18:00 +0200
            Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Andy Lutomirski <luto@amacapital.net> - 2016-07-22 23:50 +0200
              Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 00:30 +0200
                Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Andy Lutomirski <luto@amacapital.net> - 2016-07-23 01:20 +0200
                Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Andy Lutomirski <luto@amacapital.net> - 2016-07-23 01:40 +0200
                Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 02:10 +0200
                Re: [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 01:40 +0200
  [PATCH 08/19] x86/dumpstack: don't disable preemption in show_stack_log_lvl() and dump_trace() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 14/19] oprofile/x86: convert x86_backtrace() to the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 06/19] x86/dumpstack: remove extra brackets around "EOE" Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
    Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Andy Lutomirski <luto@amacapital.net> - 2016-07-23 01:30 +0200
      Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Andy Lutomirski <luto@amacapital.net> - 2016-07-23 02:00 +0200
        Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 15:10 +0200
      Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 02:00 +0200
        Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Andy Lutomirski <luto@amacapital.net> - 2016-07-23 02:20 +0200
          Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 16:10 +0200
  [PATCH 01/19] x86/dumpstack: remove show_trace() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
    Re: [PATCH 01/19] x86/dumpstack: remove show_trace() Andy Lutomirski <luto@amacapital.net> - 2016-07-22 00:00 +0200
  [PATCH 12/19] perf/x86: convert perf_callchain_kernel() to the new unwinder Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 02/19] x86/dumpstack: add get_stack_pointer() and get_frame_pointer() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
    Re: [PATCH 02/19] x86/dumpstack: add get_stack_pointer() and get_frame_pointer() Andy Lutomirski <luto@amacapital.net> - 2016-07-22 00:00 +0200
  [PATCH 11/19] x86/dumptrace: add new unwind interface and implementations Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
  [PATCH 09/19] x86/dumpstack: simplify in_exception_stack() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
    Re: [PATCH 09/19] x86/dumpstack: simplify in_exception_stack() Andy Lutomirski <luto@amacapital.net> - 2016-07-22 00:10 +0200
  [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK_SIZE define Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-21 23:30 +0200
    Re: [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK_SIZE define Andy Lutomirski <luto@amacapital.net> - 2016-07-22 00:10 +0200
      Re: [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK_SIZE define Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-22 03:50 +0200
        Re: [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK_SIZE define Ingo Molnar <mingo@kernel.org> - 2016-07-22 10:30 +0200
  Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Linus Torvalds <torvalds@linux-foundation.org> - 2016-07-23 02:30 +0200
    Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Andy Lutomirski <luto@amacapital.net> - 2016-07-23 02:40 +0200
      Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 07:40 +0200
        Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Linus Torvalds <torvalds@linux-foundation.org> - 2016-07-23 07:50 +0200
          Re: [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-23 15:00 +0200

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