Aw: RE: [OpenAFS] compile fails kernel version 4.4.0-1-default

[Benjamin Kaduk]

Presumably.  But no one seems to have reproduced the necessary conditions
in a way that allowed the root cause to be tracked down until now, so it
went unnoticed.

-Ben

On Mon, 7 Mar 2016, Stephen Joyce wrote:

> I'm no C programmer, but from my rudimentary reading of the code, wasn't there
> always a chance for -ERESTARTSYS to be returned from inside the while() loop
> inside splice_from_pipe_next(...)?
>
> On Mon, 7 Mar 2016, Benjamin Kaduk wrote:
>
> > On Thu, 3 Mar 2016, Michael Dressel wrote:
> >
> > > Hi,
> > >
> > > it is me who reported the issue on archlinux. Let me know if I can help
> > > with reproducing the issue or anything else.
> > > For curiosity, could anyone explain to me what change in the 4.4 kernel
> > > created the issue for openafs? Or rather what was the intention of the
> > > change in 4.4?
> >
> > I am given to understand that the proximal trigger is linux commit
> > http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c725bfce7968009756ed2836a8cd7ba4dc163011,
> > which addds a path wherein -ERESTARTSYS can be returned from within VFS
> > library code.  (Maybe there are other such paths, but we maybe just didn't
> > notice before?)  This particular function, splice_from_pipe_next(), ends
> > up getting called from the low-level afs_linux_storeproc() routine.  There
> > are many call paths in the cache manager that end up at this function,
> > most of which are not prepared to properly handle an ERESTARTSYS return.
> > Since this status can be returned after some data has already been
> > written, the correct behavior upon receiving it is far from clear ... a
> > path towards a client free of this vector for data corruption may involve
> > avoiding the dependence on splice_from_pipe_next() in preference to
> > adopting all call sites to handle the ERSTARTSYS case.
> >
> > -Ben
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> >
>