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Subject[PATCH] [188/275] x86/mm: Handle mm_fault_error() in kernel space
Date
2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Andrey Vagin <avagin@openvz.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@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <201103092322.p29NMNPH001682@imap1.linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.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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