Re: kvm deadlock

From: Marcelo Tosatti
Date: Wed Dec 14 2011 - 09:03:55 EST


On Wed, Dec 14, 2011 at 03:43:09PM +0200, Avi Kivity wrote:
> On 12/14/2011 02:25 PM, Marcelo Tosatti wrote:
> > On Mon, Dec 05, 2011 at 04:48:16PM -0600, Nate Custer wrote:
> > > Hello,
> > >
> > > I am struggling with repeatable full hardware locks when running 8-12 KVM vms. At some point before the hard lock I get a inconsistent lock state warning. An example of this can be found here:
> > >
> > > http://pastebin.com/8wKhgE2C
> > >
> > > After that the server continues to run for a while and then starts its death spiral. When it reaches that point it fails to log anything further to the disk, but by attaching a console I have been able to get a stack trace documenting the final implosion:
> > >
> > > http://pastebin.com/PbcN76bd
> > >
> > > All of the cores end up hung and the server stops responding to all input, including SysRq commands.
> > >
> > > I have seen this behavior on two machines (dual E5606 running Fedora 16) both passed cpuburnin testing and memtest86 scans without error.
> > >
> > > I have reproduced the crash and stack traces from a Fedora debugging kernel - 3.1.2-1 and with a vanilla 3.1.4 kernel.
> >
> > Busted hardware, apparently. Can you reproduce these issues with the
> > same workload on different hardware?
>
> I don't think it's hardware related. The second trace (in the first
> paste) is called during swap, so GFP_FS is set. The first one is not,
> so GFP_FS is clear. Lockdep is worried about the following scenario:
>
> acpi_early_init() is called
> calls pcpu_alloc(), which takes pcpu_alloc_mutex
> eventually, calls kmalloc(), or some other allocation function
> no memory, so swap
> call try_to_free_pages()
> submit_bio()
> blk_throtl_bio()
> blkio_alloc_blkg_stats()
> alloc_percpu()
> pcpu_alloc(), which takes pcpu_alloc_mutex
> deadlock
>
> It's a little unlikely that acpi_early_init() will OOM, but lockdep
> doesn't know that. Other callers of pcpu_alloc() could trigger the same
> thing.
>
> When lockdep says
>
> [ 5839.924953] other info that might help us debug this:
> [ 5839.925396] Possible unsafe locking scenario:
> [ 5839.925397]
> [ 5839.925840] CPU0
> [ 5839.926063] ----
> [ 5839.926287] lock(pcpu_alloc_mutex);
> [ 5839.926533] <Interrupt>
> [ 5839.926756] lock(pcpu_alloc_mutex);
> [ 5839.926986]
>
> It really means
>
> <swap, set GFP_FS>
>
> GFP_FS simply marks the beginning of a nested, unrelated context that
> uses the same thread, just like an interrupt. Kudos to lockdep for
> catching that.
>
> I think the allocation in blkio_alloc_blkg_stats() should be moved out
> of the I/O path into some init function. Copying Jens.

The other traces have apparently bogus NMI interrupts, but it might be a
software bug, OK.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/