cvs commit: src/sys/kern kern_sig.c

[Bruce Evans]

On Sat, 25 Oct 2003, Alfred Perlstein top posted:

> This is bad, it's time to add a flag to the vnode to do this
> properly instead of relying upon the underlying FS to implement
> the locking.

How would a mere flag help fix the real complexities for nfs?

> * Robert Watson <rwatson at FreeBSD.org> [031025 09:14] wrote:
> > rwatson     2003/10/25 09:14:09 PDT
> >
> >   FreeBSD src repository
> >
> >   Modified files:
> >     sys/kern             kern_sig.c
> >   Log:
> >   When generate a core dump, use advisory locking in an advisory way:
> >   if we do acquire an advisory lock, great!  We'll release it later.
> >   However, if we fail to acquire a lock, we perform the coredump
> >   anyway.

Er, advisory locking means that honoring the lock is not enforced, not
that it is good to not honor it.

> >   This problem became particularly visible with NFS after
> >   the introduction of rpc.lockd: if the lock manager isn't running,
> >   then locking calls will fail, aborting the core dump (resulting in
> >   a zero-byte dump file).
> >
> >   Reported by:    Yogeshwar Shenoy <ynshenoy at alumni.cs.ucsb.edu>

There is only a problem if the lock manager is supposed to be running
but is not.  That is a configuration error, or perhaps a transient error,
so it should not be "fixed" by ignoring the failure.  If ignoring nfs
locks is what is wanted in all cases, then it should be configured by
mounting the file system with -L (= nolockd).  Maybe the lock request
should hang for transient failures.

Support for correct configuration of this is still mostly nonexistent
in /etc/defaults/rc.conf and rc.conf(5).  The default for nfs mounts is
lockd, but the default for rpc_lockd_enable is "NO".  Setting
rpc_lockd_enable to "YES" is not sufficient to configure this.  The
setting of at least rc_statd_enable must also be changed.

This stuff is misconfigured on all of the freebsd machines that I
checked.  Some run 4.9, so nfs locking is not available.  beast and
builder demonstrate the bug by giving empty core dumps.  bento avoids
the bug by dumping cores in a non-nfs directory.

Bruce