On Mon, 2013-01-21 at 15:50 +0000, Myklebust, Trond wrote: > On Mon, 2013-01-21 at 15:01 +0000, Alex Bligh wrote: > > Trond, > > > > --On 21 January 2013 14:38:20 +0000 "Myklebust, Trond" > > <Trond.Myklebust@xxxxxxxxxx> wrote: > > > > > The Oops would be due to a bug in the socket layer: the socket is > > > supposed to take a reference count on the page in order to ensure that > > > it can copy the contents. > > > > Looking at the original linux-nfs link, you said here: > > http://marc.info/?l=linux-nfs&m=122424789508577&w=2 > > > > Trond:> I don't see how this could be an RPC bug. The networking > > Trond:> layer is supposed to either copy the data sent to the socket, > > Trond:> or take a reference to any pages that are pushed via > > Trond:> the ->sendpage() abi. > > > > which sounds suspiciously like the same thing. > > > > The conversation then went: > > http://marc.info/?l=linux-nfs&m=122424858109731&w=2 > > Ian:> The pages are still referenced by the networking layer. The problem is > > Ian:> that the userspace app has been told that the write has completed so > > Ian:> it is free to write new data to those pages. > > > > To which you replied: > > http://marc.info/?l=linux-nfs&m=122424984612130&w=2 > > Trond:> OK, I see your point. > > The original thread did not AFAICR involve an Oops. If you are seeing an > Oops, then that is something new and would be a socket level bug. The oops would be Xen specific, in the case where on native you would touch the buffer after a write completed and potentially resend changed data on Xen you would see an unmapped addresss. The underlying issue is the same, just the consequence on Xen is a bit more obvious. [...] > > I don't think QEMU is actually using O_DIRECT unless I set cache=none > > on the drive. That causes a different interesting failure which isn't > > my focus just now! > > Then your reference to Ian's bug is a red herring. Agreed, if there is no zero copy going on then this is a separate issue. Ian. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
