linux-kernel - [PATCH] [188/275] x86/mm: Handle mm_fault

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Message-Id: <20110330210711.A34603E1A05@tassilo.jf.intel.com>
Date:	Wed, 30 Mar 2011 14:07:11 -0700 (PDT)
From:	Andi Kleen <andi@...stfloor.org>
To:	avagin@...nvz.org, akpm@...ux-foundation.org, ak@...ux.intel.com,
	hpa@...or.com, torvalds@...ux-foundation.org, mingo@...e.hu,
	gregkh@...e.de, linux-kernel@...r.kernel.org, stable@...nel.org,
	tim.bird@...sony.com
Subject: [PATCH] [188/275] x86/mm: Handle mm_fault_error() in kernel space

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Andrey Vagin <avagin@...nvz.org>

commit f86268549f424f83b9eb0963989270e14fbfc3de upstream.

mm_fault_error() should not execute oom-killer, if page fault
occurs in kernel space.  E.g. in copy_from_user()/copy_to_user().

This would happen if we find ourselves in OOM on a
copy_to_user(), or a copy_from_user() which faults.

Without this patch, the kernels hangs up in copy_from_user(),
because OOM killer sends SIG_KILL to current process, but it
can't handle a signal while in syscall, then the kernel returns
to copy_from_user(), reexcute current command and provokes
page_fault again.

With this patch the kernel return -EFAULT from copy_from_user().

The code, which checks that page fault occurred in kernel space,
has been copied from do_sigbus().

This situation is handled by the same way on powerpc, xtensa,
tile, ...

Signed-off-by: Andrey Vagin <avagin@...nvz.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
LKML-Reference: <201103092322.p29NMNPH001682@...p1.linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/x86/mm/fault.c |    7 +++++++
 1 file changed, 7 insertions(+)

Index: linux-2.6.35.y/arch/x86/mm/fault.c
===================================================================
--- linux-2.6.35.y.orig/arch/x86/mm/fault.c	2011-03-29 22:50:46.520068086 -0700
+++ linux-2.6.35.y/arch/x86/mm/fault.c	2011-03-29 23:03:02.185244254 -0700
@@ -831,6 +831,13 @@
 	       unsigned long address, unsigned int fault)
 {
 	if (fault & VM_FAULT_OOM) {
+		/* Kernel mode? Handle exceptions or die: */
+		if (!(error_code & PF_USER)) {
+			up_read(&current->mm->mmap_sem);
+			no_context(regs, error_code, address);
+			return;
+		}
+
 		out_of_memory(regs, error_code, address);
 	} else {
 		if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON))
--
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