From: Garrick Staples <garrick@usc.edu>
Subject: Re: rpc.mountd stops functioning
Date: Sat, 28 Aug 2004 10:20:12 -0700
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On Fri, Aug 27, 2004 at 07:16:54PM -0400, J. Bruce Fields alleged:
> On Fri, Aug 27, 2004 at 01:31:20PM +1000, Neil Brown wrote:
> > I don't think this patch is needed (though it wouldn't actually break a=
nything).
> > The loop in svc_run.c starts:
> >=20
> >=20
> > 		readfds =3D svc_fdset;
> > 		cache_set_fds(&readfds);
> >=20
> > so readfds is completely initialised at the top of the loop, so
> > clearing something at the bottom (which is essentially what this patch
> > does) should be a no-op.
> >=20
> > Am I wrong?
>=20
> Note that cache_process_req() (which the patch below modifies) is not
> all the way at the bottom of the loop; there's still an importan call to
> svc_getreqset() after it.
>=20
> If I understand the problem correctly, what happens is that if select()
> returns with a set that includes two file descriptors, the first for a
> cache channel and the second for an rpc socket, and if we don't clear
> the first file descriptor from that set before passing it to
> svc_getreqset(), then the rpc code will try to read an rpc request from
> a cache channel file, and will get very confused.
>=20
> The symptom is that mountd may die occasionally on a server that's
> using the new interface (hence mountd is handling upcalls), and that's
> getting a lot of mount requests.

Yes, this is exactly what happens.  The RPC code reading from the cache cha=
nnel
file segfaults mountd every time.

On my two main fileservers, mountd would die every few hours.  Sometimes,
conditions being optimal to trigger the bug, it would chain-crash.  It hasn=
't
segfaulted at all since that one line patch.

I'm surprised more people haven't reported this segfault.  I guess not many
people are using the new interface in heavy production.

--=20
Garrick Staples, Linux/HPCC Administrator
University of Southern California

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