On Mon, Aug 05, 2013 at 03:06:18PM -0700, Andrew Morton wrote:
> On Sat, 3 Aug 2013 12:59:56 -0400 Johannes Weiner <han...@cmpxchg.org> wrote:
>
> > Unlike global OOM handling, memory cgroup code will invoke the OOM
> > killer in any OOM situation because it has no way of telling faults
> > occuring in kernel context - which could be handled more gracefully -
> > from user-triggered faults.
> >
> > Pass a flag that identifies faults originating in user space from the
> > architecture-specific fault handlers to generic code so that memcg OOM
> > handling can be improved.
>
> arch/arm64/mm/fault.c has changed. Here's what I came up with:
>
> ---
> a/arch/arm64/mm/fault.c~arch-mm-pass-userspace-fault-flag-to-generic-fault-handler
> +++ a/arch/arm64/mm/fault.c
> @@ -199,13 +199,6 @@ static int __kprobes do_page_fault(unsig
> unsigned long vm_flags = VM_READ | VM_WRITE | VM_EXEC;
> unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
>
> - if (esr & ESR_LNX_EXEC) {
> - vm_flags = VM_EXEC;
> - } else if ((esr & ESR_WRITE) && !(esr & ESR_CM)) {
> - vm_flags = VM_WRITE;
> - mm_flags |= FAULT_FLAG_WRITE;
> - }
> -
> tsk = current;
> mm = tsk->mm;
>
> @@ -220,6 +213,16 @@ static int __kprobes do_page_fault(unsig
> if (in_atomic() || !mm)
> goto no_context;
>
> + if (user_mode(regs))
> + mm_flags |= FAULT_FLAG_USER;
> +
> + if (esr & ESR_LNX_EXEC) {
> + vm_flags = VM_EXEC;
> + } else if ((esr & ESR_WRITE) && !(esr & ESR_CM)) {
> + vm_flags = VM_WRITE;
> + mm_flags |= FAULT_FLAG_WRITE;
> + }
> +
> /*
> * As per x86, we may deadlock here. However, since the kernel only
> * validly references user space from well defined areas of the code,
>
> But I'm not terribly confident in it.
It looks good to me. They added the vm_flags but they are not used
any earlier than the mm_flags (__do_page_fault), which I moved to the
same location as you did in this fixup.
Thanks!
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