Re: [PATCH 24/25] r/o bind mounts: track number of mount writers - Kernel

This is a discussion on Re: [PATCH 24/25] r/o bind mounts: track number of mount writers - Kernel ; On Sun, 2007-09-23 at 23:17 -0700, Andrew Morton wrote: > It look like a false positive to me, but really, for a patchset of this > complexity and maturity I cannot fathom how it could have escaped any > lockdep ...

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Thread: Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

  1. Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

    On Sun, 2007-09-23 at 23:17 -0700, Andrew Morton wrote:
    > It look like a false positive to me, but really, for a patchset of this
    > complexity and maturity I cannot fathom how it could have escaped any
    > lockdep testing.


    I test with lockdep all the time. The problem was that lockdep doesn't
    complain until you have 8 nested locks, and I only tested on a 4-cpu
    system.

    I lowered the lockdep nesting limit to 3, and got the warning on my
    machine.

    -- Dave

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  2. Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

    On Mon, 24 Sep 2007 15:06:42 -0700
    Dave Hansen wrote:

    > On Sun, 2007-09-23 at 23:17 -0700, Andrew Morton wrote:
    > > It look like a false positive to me, but really, for a patchset of this
    > > complexity and maturity I cannot fathom how it could have escaped any
    > > lockdep testing.

    >
    > I test with lockdep all the time. The problem was that lockdep doesn't
    > complain until you have 8 nested locks, and I only tested on a 4-cpu
    > system.
    >
    > I lowered the lockdep nesting limit to 3, and got the warning on my
    > machine.
    >


    hm. I saw that warning on my 2-way. It has CONFIG_NR_CPUS=8 so perhaps
    the kernel has decided that this machine can possibly have eight CPUs.

    It's an old super-micro board, doesn't have ACPI.

    OEM ID: INTEL Product ID: 440BX APIC at: 0xFEE00000
    Processor #0 6:8 APIC version 17
    Processor #1 6:8 APIC version 17
    I/O APIC #2 Version 17 at 0xFEC00000.
    Enabling APIC mode: Flat. Using 1 I/O APICs
    Processors: 2

    ....

    Checking if this processor honours the WP bit even in supervisor mode... Ok.
    Calibrating delay using timer specific routine.. 1707.03 BogoMIPS (lpj=3414067)
    Mount-cache hash table entries: 512
    CPU: After generic identify, caps: 0383fbff 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    CPU: L1 I cache: 16K, L1 D cache: 16K
    CPU: L2 cache: 256K
    CPU: After all inits, caps: 0383fbff 00000000 00000000 00000040 00000000 00000000 00000000 00000000
    Intel machine check architecture supported.
    Intel machine check reporting enabled on CPU#0.
    Compat vDSO mapped to ffffe000.
    Checking 'hlt' instruction... OK.
    lockdep: not fixing up alternatives.
    CPU0: Intel Pentium III (Coppermine) stepping 03
    lockdep: not fixing up alternatives.
    Booting processor 1/1 eip 2000
    Initializing CPU#1
    Calibrating delay using timer specific routine.. 1704.02 BogoMIPS (lpj=3408054)
    CPU: After generic identify, caps: 0383fbff 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    CPU: L1 I cache: 16K, L1 D cache: 16K
    CPU: L2 cache: 256K
    CPU: After all inits, caps: 0383fbff 00000000 00000000 00000040 00000000 00000000 00000000 00000000
    Intel machine check architecture supported.
    Intel machine check reporting enabled on CPU#1.
    CPU1: Intel Pentium III (Coppermine) stepping 03
    Total of 2 processors activated (3411.06 BogoMIPS).
    ExtINT not setup in hardware but reported by MP table
    ENABLING IO-APIC IRQs
    ...TIMER: vector=0x31 apic1=0 pin1=2 apic2=0 pin2=0
    APIC timer registered as dummy, due to nmi_watchdog=1!
    checking TSC synchronization [CPU#0 -> CPU#1]: passed.
    Brought up 2 CPUs


    One would think that the kernel would work out that eight CPUs ain't
    possible on such a machine. But we don't seem to print out any info which
    allows me to confirm that this is really what the kernel did.


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  3. Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

    On Mon, 2007-09-24 at 15:25 -0700, Andrew Morton wrote:
    > hm. I saw that warning on my 2-way. It has CONFIG_NR_CPUS=8 so perhaps
    > the kernel has decided that this machine can possibly have eight CPUs.
    >
    > It's an old super-micro board, doesn't have ACPI.


    Well, it's looking like we only set cpu_possible_map from data we find
    in the MP table, which makes sense. The only question is how your
    system gets more than ~8 possible cpus. Do you have the .config handy?

    -- Dave

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  4. Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

    On Mon, 24 Sep 2007 16:05:37 -0700
    Dave Hansen wrote:

    > On Mon, 2007-09-24 at 15:25 -0700, Andrew Morton wrote:
    > > hm. I saw that warning on my 2-way. It has CONFIG_NR_CPUS=8 so perhaps
    > > the kernel has decided that this machine can possibly have eight CPUs.
    > >
    > > It's an old super-micro board, doesn't have ACPI.

    >
    > Well, it's looking like we only set cpu_possible_map from data we find
    > in the MP table, which makes sense. The only question is how your
    > system gets more than ~8 possible cpus. Do you have the .config handy?
    >


    http://userweb.kernel.org/~akpm/config-vmm.txt
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  5. Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

    On Mon, 2007-09-24 at 16:15 -0700, Andrew Morton wrote:
    > On Mon, 24 Sep 2007 16:05:37 -0700
    > Dave Hansen wrote:
    >
    > > On Mon, 2007-09-24 at 15:25 -0700, Andrew Morton wrote:
    > > > hm. I saw that warning on my 2-way. It has CONFIG_NR_CPUS=8 so perhaps
    > > > the kernel has decided that this machine can possibly have eight CPUs.
    > > >
    > > > It's an old super-micro board, doesn't have ACPI.

    > >
    > > Well, it's looking like we only set cpu_possible_map from data we find
    > > in the MP table, which makes sense. The only question is how your
    > > system gets more than ~8 possible cpus. Do you have the .config handy?

    >
    > http://userweb.kernel.org/~akpm/config-vmm.txt


    I've reproduced this. I'll do more runtime testing with all of the
    debugging, CONFIG_CPU_HOTPLUG=y, and NR_CPUS to a high value. It should
    help catch things like this in the future.

    -- Dave

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