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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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