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Date: Fri, 17 Jan 2014 15:08:13 -0500
From: Waiman Long <waiman.long@hp.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Scott J Norton <scott.norton@hp.com>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        tip-bot for Peter Zijlstra <tipbot@zytor.com>,
        linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] x86, mm, perf: Allow recursive faults from interrupts
References: <20140110200603.GJ7572@laptop.programming.kicks-ass.net> <tip-c026b3591e4f2a4993df773183704bb31634e0bd@git.kernel.org> <52D971FE.9030008@hp.com> <CALCETrWF4AwFrBrA1WdrEUj5=oPfiPPUF7PJCooagTi6Y07Pwg@mail.gmail.com>
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On 01/17/2014 02:17 PM, Andy Lutomirski wrote:
> On Fri, Jan 17, 2014 at 10:10 AM, Waiman Long<waiman.long@hp.com>  wrote:
>> On 01/16/2014 08:39 AM, tip-bot for Peter Zijlstra wrote:
>>> Commit-ID:  c026b3591e4f2a4993df773183704bb31634e0bd
>>> Gitweb:
>>> http://git.kernel.org/tip/c026b3591e4f2a4993df773183704bb31634e0bd
>>> Author:     Peter Zijlstra<peterz@infradead.org>
>>> AuthorDate: Fri, 10 Jan 2014 21:06:03 +0100
>>> Committer:  Ingo Molnar<mingo@kernel.org>
>>> CommitDate: Thu, 16 Jan 2014 09:19:48 +0100
>>>
>>> x86, mm, perf: Allow recursive faults from interrupts
>>>
>>> Waiman managed to trigger a PMI while in a emulate_vsyscall() fault,
>>> the PMI in turn managed to trigger a fault while obtaining a stack
>>> trace. This triggered the sig_on_uaccess_error recursive fault logic
>>> and killed the process dead.
>>>
>>> Fix this by explicitly excluding interrupts from the recursive fault
>>> logic.
>>>
>>> Reported-and-Tested-by: Waiman Long<waiman.long@hp.com>
>>> Fixes: e00b12e64be9 ("perf/x86: Further optimize copy_from_user_nmi()")
>>> Cc: Aswin Chandramouleeswaran<aswin@hp.com>
>>> Cc: Scott J Norton<scott.norton@hp.com>
>>> Cc: Linus Torvalds<torvalds@linux-foundation.org>
>>> Cc: Andy Lutomirski<luto@amacapital.net>
>>> Cc: Arnaldo Carvalho de Melo<acme@ghostprotocols.net>
>>> Cc: Andrew Morton<akpm@linux-foundation.org>
>>> Signed-off-by: Peter Zijlstra<peterz@infradead.org>
>>> Link:
>>> http://lkml.kernel.org/r/20140110200603.GJ7572@laptop.programming.kicks-ass.net
>>> Signed-off-by: Ingo Molnar<mingo@kernel.org>
>>> ---
>>>    arch/x86/mm/fault.c | 18 ++++++++++++++++++
>>>    1 file changed, 18 insertions(+)
>>>
>>>
>> Will that be picked up by Linus as it is a 3.13 regression?
> Does anyone actually know why this regressed recently?  The buggy code
> has been there for quite a while.
>
> --Andy

Yes, the bug was there for a while, but a recent change by Peter (see 
the "Fixes:" line above) made it much easier to hit it.

-Longman