linux-kernel - Re: [PATCH] x86, syscall: Fix _TIF_NOHZ handling in syscall_trace_enter

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Message-ID: <alpine.DEB.2.11.1411192311560.3909@nanos>
Date:	Wed, 19 Nov 2014 23:13:53 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86, syscall: Fix _TIF_NOHZ handling in
 syscall_trace_enter_phase1

On Wed, 19 Nov 2014, Andy Lutomirski wrote:

> TIF_NOHZ is 19 (i.e. _TIF_SYSCALL_TRACE | _TIF_NOTIFY_RESUME |
> _TIF_SINGLESTEP), not (1<<19).
> 
> This code is involved in Dave's trinity lockup, but I don't see why
> it would cause any of the problems he's seeing, except inadvertently
> by causing a different path through entry_64.S's syscall handling.

Right, while it is wrong it does not explain the wreckage on 3.17,
which does not have that code.

Thanks,

	tglx
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