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    SubjectRe: frequent lockups in 3.18rc4
    On Nov 21, 2014 8:27 AM, "Tejun Heo" <tj@kernel.org> wrote:
    >
    > Hello, Andy.
    >
    > On Thu, Nov 20, 2014 at 03:55:09PM -0800, Andy Lutomirski wrote:
    > > That doesn't appear to have anything to with nmi though, right?
    >
    > I thought that was the main offender but, apparently, not any more.
    >
    > > Wouldn't this issue be fixed by moving the vmalloc_fault check into
    > > do_page_fault before exception_enter?
    >
    > Can you please elaborate why that'd fix the issue? I'm not
    > intimiately familiar with the fault handling so it'd be great if you
    > can give me some pointers in terms of where to look at.

    do_page_fault is called directly from asm. It does:

    prev_state = exception_enter();
    __do_page_fault(regs, error_code, address);
    exception_exit(prev_state);

    The vmalloc fixup is in __do_page_fault.

    exception_enter does various accounting and tracing things, and I
    think that the recursion in stack trace I saw was in exception_enter.

    If you move the vmalloc fixup before exception_enter() and return if
    the fault was from vmalloc, then you can't recurse. You need to be
    careful not to touch anything that uses RCU before exception_enter,
    though.

    --Andy

    >
    > Thanks.
    >
    > --
    > tejun


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