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Subject: Re: [2.6.25-rc5-mm1] BUG: spinlock bad magic early during boot
From: Dave Hansen <haveblue@us.ibm.com>
To: Tilman Schmidt <tilman@imap.cc>
Cc: Eric Piel <eric.piel@tremplin-utc.net>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Thomas Renninger <trenn@suse.de>, Len Brown <len.brown@intel.com>,
       Linus Torvalds <torvalds@osdl.org>,
       Christoph Hellwig <hch@infradead.org>,
       Markus Gaugusch <dsdt@gaugusch.at>, linux-acpi@vger.kernel.org,
       Al Viro <viro@ZenIV.linux.org.uk>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
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Date: Sun, 16 Mar 2008 13:11:19 -0700
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On Sat, 2008-03-15 at 13:47 +0100, Tilman Schmidt wrote:
> > Anyway, I'm sick of too much bitching and too little coding.
> Andrew,
> > here's a patch for -mm that will at least shut up the spinlock
> warnings.
> 
> Sorry to say, it doesn't. That is, it does shut up the warning I
> reported, but there's a new one appearing now instead, three lines
> later. Here's the dmesg diff:
> 
> @@ -216,29 +216,30 @@
>  CPU0: Thermal monitoring enabled
>  Compat vDSO mapped to ffffe000.
>  Checking 'hlt' instruction... OK.
> -BUG: spinlock bad magic on CPU#0, swapper/0
> - lock: c2c19380, .magic: 00000000, .owner: swapper/0, .owner_cpu: 0
> -Pid: 0, comm: swapper Not tainted 2.6.25-rc5-mm1-testing #2
> - [<c01f728c>] spin_bug+0x7c/0x87
> - [<c01f72b0>] _raw_spin_unlock+0x19/0x71
> - [<c0301922>] _spin_unlock+0x1d/0x3c
> - [<c01981aa>] mnt_want_write+0x62/0x88
> - [<c018c382>] sys_mkdirat+0x86/0xd6
> - [<c04260ab>] ? clean_path+0x16/0x4a
> - [<c017fd6f>] ? kfree+0xd8/0xec
> - [<c018c3e2>] sys_mkdir+0x10/0x12
> - [<c0426353>] do_name+0x112/0x1b3
> - [<c042558b>] write_buffer+0x1d/0x2c
> - [<c04255fe>] flush_window+0x64/0xb3
> - [<c04272f5>] unpack_to_rootfs+0x62c/0x8b9
> - [<c04275a2>] populate_rootfs+0x20/0x109
> - [<c0429ed2>] ? alternative_instructions+0x153/0x158
> - [<c04248f5>] start_kernel+0x343/0x355
> - [<c0424019>] i386_start_kernel+0x8/0xa
> - =======================
>  Unpacking initramfs... done
> -Freeing initrd memory: 8767k freed
> +Freeing initrd memory: 8834k freed
>  ACPI: Core revision 20070126
> +INFO: trying to register non-static key.
> +the code is fine but needs lockdep annotation.
> +turning off the locking correctness validator.
> +Pid: 0, comm: swapper Not tainted 2.6.25-rc5-mm1-testing #3
> + [<c014321e>] __lock_acquire+0x144/0xb6e
> + [<c010b1a2>] ? native_sched_clock+0xe0/0xff
> + [<c017fc57>] ? kmem_cache_alloc+0x89/0xc9
> + [<c0142ce0>] ? trace_hardirqs_on+0xe8/0x11d
> + [<c014404f>] lock_acquire+0x6a/0x90
> + [<c013b460>] ? down_trylock+0xc/0x27
> + [<c03016cb>] _spin_lock_irqsave+0x42/0x72
> + [<c013b460>] ? down_trylock+0xc/0x27
> + [<c013b460>] down_trylock+0xc/0x27
> + [<c021fa65>] acpi_os_wait_semaphore+0x67/0x13d
> + [<c023a39e>] acpi_ut_acquire_mutex+0x65/0xcf
> + [<c0230261>] acpi_ns_root_initialize+0x1a/0x289
> + [<c043ad54>] acpi_initialize_subsystem+0x47/0x6a
> + [<c043afd4>] acpi_early_init+0x57/0xf8
> + [<c04248ff>] start_kernel+0x34d/0x35a
> + [<c0424019>] i386_start_kernel+0x8/0xa
> + =======================
>  ACPI: Checking initramfs for custom DSDT
>  Parsing all Control Methods:
>  Table [DSDT](id 0001) - 637 Objects with 63 Devices 160 Methods 41
> Regions

Hi Tim,

Again, thanks for the excellent bug reporting. 

This is actually a different problem (and not my code again, thank
goodness).  I think a few of these got fixed in current -mm.  According
to Peter Z, these mean:

> It means the lock_class_key ended up in non-static storage.
> 
> In practise it often means you initialized a on-stack structure
> incorrectly. DECLARE_WAIT_QUEUE_HEAD() vs
> DECLARE_WAIT_QUEUE_HEAD_ONSTACK() for example.

So, this looks like an on-stack ACPI structure that got initialized
wrongly.  At least we already have those dudes on the cc. :)

But, this might also get fixed by reverting the patch as Linus just did.
It might just be best to wait for another -mm release and see how it
settles out.  

-- Dave

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