[PATCH] [188/275] x86/mm: Handle mm_fault_error() in kernel space

[Andi Kleen]

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

------------------
From: Andrey Vagin <avagin@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
LKML-Reference: <201103092322.p29NMNPH001682@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 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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