linux-kernel - Re: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc

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Message-ID: <20131016061118.GA21109@gmail.com>
Date:	Wed, 16 Oct 2013 08:11:18 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>,
	"Li, Zhuangzhi" <zhuangzhi.li@...el.com>,
	"Liu, Chuansheng" <chuansheng.liu@...el.com>
Subject: Re: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc_fault


* Steven Rostedt <rostedt@...dmis.org> wrote:

> Since the NMI iretq nesting has been fixed, there's no reason that
> an NMI handler can not take a page fault for vmalloc'd code. No locks
> are taken in that code path, and the software now handles nested NMIs
> when the fault re-enables NMIs on iretq.
> 
> Not only that, if the vmalloc_fault() WARN_ON_ONCE() is hit, and that
> warn on triggers a vmalloc fault for some reason, then we can go into
> an infinite loop (the WARN_ON_ONCE() does the WARN() before updating
> the variable to make it happen "once").
> 
> Reported-by: "Liu, Chuansheng" <chuansheng.liu@...el.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Would be nice to see the warning quoted that triggered this.

Thanks,

	Ingo
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