Re: [Xen-devel] blkfront problem in pvops kernel when barriers enabled

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sun, Sep 04, 2011 at 12:49:42PM +0200, Marek Marczykowski wrote:
> Hello,
> 
> Pvops block frontend (tested vanilla 3.0.3, 3.1rc2, Konrad's testing
> branch) produces a lot of I/O errors when barriers are enabled but
> cannot be used.
> 
> On xenlinux I've got message:
> [   15.036921] blkfront: xvdb: empty write barrier op failed
> [   15.036936] blkfront: xvdb: barriers disabled
> 
> and after that, everything works fine. On pvops - I/O errors.
> As backend I've used 2.6.38.3 xenlinux (based on SUSE package) and
> 3.1rc2 with same result.

Hm, and the 'feature-barrier' was enabled on in those backends?
That is really bizzare considering that those backends don't actually
support WRITE_BARRIER anymore.

> 
> When I disable barriers (patching blkbackend to set feature-barrier=0)
> everything works fine with all above versions.

Ok, and the patch you sent "[PATCH] Initialize vars in blkfront_connect"
as well?

> 
> My setup is xen-4.1.1 (if it matters), backends: phy from device-mapper
> device and phy from loop device; frontends covered by device-mapper
> snapshot, which is set up in domU initramfs.
> 
> It looks like some race condition, because when I setup device-mapper in
> domU and mount it manually (which cause some delays between steps), it
> works fine...
> 
> Have you idea why it happens? What additional data can I provide debug it?
> 
> In addition it should be possible to disable barrier without patching
> module... Perhaps some pciback module parameter? Or leave feature-*

Not sure why you would touch pciback.. But the barrier should _not_
be enabled in those backends. The 'feature-flush-cache' should be.


> xenstore entries alone if present before device initialization.
> 
> -- 
> Pozdrawiam / Best Regards,
> Marek Marczykowski         | RLU #390519
> marmarek at mimuw edu pl   | xmpp:marmarek at staszic waw pl
> 



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