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

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Message-ID: <20131015163906.342d8ffa@gandalf.local.home>
Date:	Tue, 15 Oct 2013 16:39:06 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...nel.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: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc_fault

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>
---
 arch/x86/mm/fault.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 3aaeffc..78926c6 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -268,8 +268,6 @@ static noinline __kprobes int vmalloc_fault(unsigned long address)
 	if (!(address >= VMALLOC_START && address < VMALLOC_END))
 		return -1;
 
-	WARN_ON_ONCE(in_nmi());
-
 	/*
 	 * Synchronize this task's top level page-table
 	 * with the 'reference' page table.
-- 
1.8.1.4

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