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

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Date:   Fri, 16 Sep 2016 07:28:16 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     tip-bot for Andy Lutomirski <tipbot@...or.com>
Cc:     linux-tip-commits@...r.kernel.org, luto@...nel.org, hpa@...or.com,
        mingo@...nel.org, dvlasenk@...hat.com,
        linux-kernel@...r.kernel.org, jann@...jh.net, peterz@...radead.org,
        torvalds@...ux-foundation.org, brgerst@...il.com,
        tglx@...utronix.de, bp@...en8.de
Subject: Re: [tip:x86/asm] x86/dumpstack: Pin the target stack when dumping it

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@...nel.org>
> > AuthorDate: Thu, 15 Sep 2016 22:45:45 -0700
> > Committer:  Ingo Molnar <mingo@...nel.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