releases/2.6.37.5/x86-mm-handle-mm_fault_error-in-kernel-space.patch

   1 From f86268549f424f83b9eb0963989270e14fbfc3de Mon Sep 17 00:00:00 2001
   2 From: Andrey Vagin <avagin@openvz.org>
   3 Date: Wed, 9 Mar 2011 15:22:23 -0800
   4 Subject: x86/mm: Handle mm_fault_error() in kernel space
   5
   6 From: Andrey Vagin <avagin@openvz.org>
   7
   8 commit f86268549f424f83b9eb0963989270e14fbfc3de upstream.
   9
  10 mm_fault_error() should not execute oom-killer, if page fault
  11 occurs in kernel space.  E.g. in copy_from_user()/copy_to_user().
  12
  13 This would happen if we find ourselves in OOM on a
  14 copy_to_user(), or a copy_from_user() which faults.
  15
  16 Without this patch, the kernels hangs up in copy_from_user(),
  17 because OOM killer sends SIG_KILL to current process, but it
  18 can't handle a signal while in syscall, then the kernel returns
  19 to copy_from_user(), reexcute current command and provokes
  20 page_fault again.
  21
  22 With this patch the kernel return -EFAULT from copy_from_user().
  23
  24 The code, which checks that page fault occurred in kernel space,
  25 has been copied from do_sigbus().
  26
  27 This situation is handled by the same way on powerpc, xtensa,
  28 tile, ...
  29
  30 Signed-off-by: Andrey Vagin <avagin@openvz.org>
  31 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  32 Cc: "H. Peter Anvin" <hpa@zytor.com>
  33 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  34 LKML-Reference: <201103092322.p29NMNPH001682@imap1.linux-foundation.org>
  35 Signed-off-by: Ingo Molnar <mingo@elte.hu>
  36 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  37
  38 ---
  39  arch/x86/mm/fault.c |    7 +++++++
  40  1 file changed, 7 insertions(+)
  41
  42 --- a/arch/x86/mm/fault.c
  43 +++ b/arch/x86/mm/fault.c
  44 @@ -827,6 +827,13 @@ mm_fault_error(struct pt_regs *regs, uns
  45                unsigned long address, unsigned int fault)
  46  {
  47         if (fault & VM_FAULT_OOM) {
  48 +               /* Kernel mode? Handle exceptions or die: */
  49 +               if (!(error_code & PF_USER)) {
  50 +                       up_read(&current->mm->mmap_sem);
  51 +                       no_context(regs, error_code, address);
  52 +                       return;
  53 +               }
  54 +
  55                 out_of_memory(regs, error_code, address);
  56         } else {
  57                 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|