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Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it

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On Fri, Sep 16, 2016 at 06:55:57AM -0500, Josh Poimboeuf wrote:
> On Fri, Sep 16, 2016 at 02:17:46AM -0700, tip-bot for Andy Lutomirski wrote:
> > Commit-ID:  1959a60182f48879635812a03a99c02231ea8677
> > Gitweb:     http://git.kernel.org/tip/1959a60182f48879635812a03a99c02231ea8677
> > Author:     Andy Lutomirski <luto@kernel.org>
> > AuthorDate: Thu, 15 Sep 2016 22:45:45 -0700
> > Committer:  Ingo Molnar <mingo@kernel.org>
> > CommitDate: Fri, 16 Sep 2016 09:18:53 +0200
> > 
> > x86/dumpstack: Pin the target stack when dumping it
> > 
> > Specifically, pin the stack in save_stack_trace_tsk() and
> > show_trace_log_lvl().
> > 
> > This will prevent a crash if the target task dies before or while
> > dumping its stack once we start freeing task stacks early.
> 
> This causes a hang:

The problem is that show_stack_log_lvl() can be called with a NULL
task_struct pointer to indicate 'current'.

No idea why that convention exists -- IMO we should just require the
caller to pass 'current' directly.

-- 
Josh

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[PATCH v2 0/8] thread_info cleanups and stack caching Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
  [PATCH v2 1/8] x86/entry/64: Fix a minor comment rebase error Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] x86/entry/64: Fix a minor comment rebase error tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:20 +0200
  [PATCH v2 4/8] x86/dumpstack: Pin the target stack when dumping it Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:20 +0200
      Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-16 14:00 +0200
        Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-16 14:30 +0200
          Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it Ingo Molnar <mingo@kernel.org> - 2016-09-16 15:00 +0200
            [PATCH] x86/dumpstack: remove NULL task pointer convention Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-16 15:10 +0200
  [PATCH v2 6/8] lib/syscall: Pin the task stack in collect_syscall() Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] lib/syscall: Pin the task stack in collect_syscall() tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:20 +0200
  [PATCH v2 8/8] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] fork: Optimize task creation by caching two thread  stacks per CPU if CONFIG_VMAP_STACK=y tip-bot for Andy Lutomirski <tipbot@zytor.com> - 2016-09-16 11:30 +0200
  [PATCH v2 3/8] kthread: to_live_kthread() needs try_get_task_stack() Andy Lutomirski <luto@kernel.org> - 2016-09-16 07:50 +0200
    [tip:x86/asm] kthread: Pin the stack via  try_get_task_stack()/put_task_stack() in to_live_kthread() function tip-bot for Oleg Nesterov <tipbot@zytor.com> - 2016-09-16 11:20 +0200

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