Re: [Xen-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 15 Mar 2013, Ian Campbell wrote:
> On Thu, 2013-03-14 at 19:30 +0000, Ian Jackson wrote:
> > Stefano Stabellini writes ("Re: [PATCHv3] QEMU(upstream): Disable xen's use 
> > of O_DIRECT by default as it results in crashes."):
> > > On Fri, 8 Mar 2013, Alex Bligh wrote:
> > > > Due to what is almost certainly a kernel bug, writes with
> > > > O_DIRECT may continue to reference the page after the write
> > > > has been marked as completed, particularly in the case of
> > > > TCP retransmit. In other scenarios, this "merely" risks
> > > > data corruption on the write, but with Xen pages from domU
> > > > are only transiently mapped into dom0's memory, resulting
> > > > in kernel panics when they are subsequently accessed.
> > > > 
> > > > This brings PV devices in line with emulated devices. Removing
> > > > O_DIRECT is safe as barrier operations are now correctly passed
> > > > through.
> > > > 
> > > > See:
> > > >   http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html
> > > > for more details.
> > > > 
> > > > Signed-off-by: Alex Bligh <alex@xxxxxxxxxxx>
> > > 
> > > 
> > > Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > 
> > Marvellous, pushed to staging/qemu-upstream-unstable.git
> 
> Isn't one of the guiding principals of this tree that it should contain
> only backports from upstream qemu.git#master? In order to avoid
> regressions in the future, accidental forking, etc etc.
> 
> I don't see this commit in upstream qemu.git and AFAICT this patch
> wasn't even sent to qemu-devel.
> 
> There may well be exceptions to this e.g. where qemu-devel is slow and
> the matter is urgent or where the issue only pertains to the stable
> branch but I don't think there are any exceptional circumstances here.

I agree. My intention was to send the patch upstream and then backport
it to qemu-upstream-unstable.

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