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

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Message-Id: <20070924152532.305ec951.akpm@linux-foundation.org>
Date:	Mon, 24 Sep 2007 15:25:32 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: [PATCH 24/25] r/o bind mounts: track number of mount writers

On Mon, 24 Sep 2007 15:06:42 -0700
Dave Hansen <haveblue@...ibm.com> 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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