linux-kernel - Re: perf: fuzzer BUG: KASAN: stack-out-of-bounds in __unwind

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Message-ID: <20161129091650.GA3092@twins.programming.kicks-ass.net>
Date:   Tue, 29 Nov 2016 10:16:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Vince Weaver <vincent.weaver@...ne.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>
Subject: Re: perf: fuzzer BUG: KASAN: stack-out-of-bounds in __unwind_start

On Mon, Nov 28, 2016 at 11:52:41PM -0600, Josh Poimboeuf wrote:
> > We used to do that, but the resulting NMIs were problematic on some
> > platforms.  Perhaps things have gotten better?
> 
> Did a little digging on git blame and found the following commit (which
> seems to be the cause of the KASAN warning and missing stack dump):
> 
>   bc1dce514e9b ("rcu: Don't use NMIs to dump other CPUs' stacks")
> 
> I presume this commit is still needed because of the NMI printk deadlock
> issues which were discussed at Kernel Summit.  I guess those issues need
> to be sorted out before the above commit can be reverted.

so printk should more or less work from NMI, esp. after:

  42a0bb3f7138 ("printk/nmi: generic solution for safe printk in NMI")