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    SubjectRe: [PATCH 4/5] UML - Simplify helper stack handling
    On Sun, 5 Aug 2007 22:41:14 +0200 Luca Tettamanti <kronos.it@gmail.com> wrote:

    > Il Wed, Jun 27, 2007 at 11:37:01PM -0700, Andrew Morton ha scritto:
    > >
    > > So I'm running the generic version of this on i386 with 8k stacks (below),
    > > with a quick LTP run.
    > >
    > > Holy cow, either we use a _lot_ of stack or these numbers are off:
    > >
    > > vmm:/home/akpm> dmesg -s 1000000|grep 'bytes left'
    > > khelper used greatest stack depth: 7176 bytes left
    > > khelper used greatest stack depth: 7064 bytes left
    > > khelper used greatest stack depth: 6840 bytes left
    > > khelper used greatest stack depth: 6812 bytes left
    > > hostname used greatest stack depth: 6636 bytes left
    > > uname used greatest stack depth: 6592 bytes left
    > > uname used greatest stack depth: 6284 bytes left
    > > hotplug used greatest stack depth: 5568 bytes left
    > > rpc.nfsd used greatest stack depth: 5136 bytes left
    > > chown02 used greatest stack depth: 4956 bytes left
    > > fchown01 used greatest stack depth: 4892 bytes left
    > >
    > > That's the sum of process stack and interrupt stack, but I doubt if this
    > > little box is using much interrupt stack space.
    > >
    > > No wonder people are still getting stack overflows with 4k stacks...
    >
    > Hi Andrew,
    > I was a bit worried about stack usage on my setup and google found your
    > mail :P
    >
    > FYI:
    >
    > khelper used greatest stack depth: 3228 bytes left
    > khelper used greatest stack depth: 3124 bytes left
    > busybox used greatest stack depth: 2808 bytes left
    > modprobe used greatest stack depth: 2744 bytes left
    > busybox used greatest stack depth: 2644 bytes left
    > modprobe used greatest stack depth: 1836 bytes left
    > modprobe used greatest stack depth: 1176 bytes left
    > java used greatest stack depth: 932 bytes left
    > java used greatest stack depth: 540 bytes left
    >
    > I'm running git-current, with 4KiB stacks; filesystems are ext3 and XFS
    > on LVM (on libata devices).
    > Does it make sense to raise STACK_WARN to get a stack trace in do_IRQ?
    > Or is 540 bytes still "safe" taking into account the separate IRQ stack?
    >

    540 bytes free means that we've used 90% of the stack. I'd say it is
    extremely unsafe.

    Unbelieveably unsafe. I'm suspecting that the instrumentation is lying to
    us for some reason.

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