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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

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.

Ian.


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