On Thu, Apr 23, 2009 at 07:33:33PM -0400, Chuck Lever wrote:
> When rpc.statd starts up in user space at boot time, it attempts to
> write the latest NSM local state number into
> /proc/sys/fs/nfs/nsm_local_state.
>
> If lockd.ko isn't loaded yet (as is the case in most configurations),
> that file doesn't exist, thus the kernel's NSM state remains set to
> its initial value of zero during lockd operation.
>
> This is a problem because rpc.statd and lockd use the NSM state number
> to prevent repeated lock recovery on rebooted hosts. If lockd sends
> a zero NSM state, but then a delayed SM_NOTIFY with a real NSM state
> number is received, there is no way for lockd or rpc.statd to
> distinguish that stale SM_NOTIFY from an actual reboot. Thus lock
> recovery could be performed after the rebooted host has already
> started reclaiming locks, and those locks will be lost.
>
> We could change /etc/init.d/nfslock so it always modprobes lockd.ko
> before starting rpc.statd. However, if lockd.ko is ever unloaded
> and reloaded, we are back at square one, since the NSM state is not
> preserved across an unload/reload cycle. This may happen frequently
> on clients that use automounter. A period of NFS inactivity causes
> lockd.ko to be unloaded, and the kernel loses its NSM state setting.
Aie. Can we also fix the automounter or some other part of the
userspace configuration?
> Instead, let's use the fact that rpc.statd plants the local system's
> NSM state in every SM_MON (and SM_UNMON) reply. lockd performs a
> synchronous SM_MON upcall to the local rpc.statd _before_ sending its
> first NLM request to a new remote. This would permit rpc.statd to
> provide the current NSM state to lockd, even after lockd.ko had been
> unloaded and reloaded.
>
> Note that NLMPROC_LOCK arguments are constructed before the
> nsm_monitor() call, so we have to rearrange argument construction very
> slightly to make this all work out.
>
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
>
> fs/lockd/clntproc.c | 2 +-
> fs/lockd/mon.c | 6 +++++-
> 2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/lockd/clntproc.c b/fs/lockd/clntproc.c
> index dd79570..f55b900 100644
> --- a/fs/lockd/clntproc.c
> +++ b/fs/lockd/clntproc.c
> @@ -126,7 +126,6 @@ static void nlmclnt_setlockargs(struct nlm_rqst *req, struct file_lock *fl)
> struct nlm_lock *lock = &argp->lock;
>
> nlmclnt_next_cookie(&argp->cookie);
> - argp->state = nsm_local_state;
> memcpy(&lock->fh, NFS_FH(fl->fl_file->f_path.dentry->d_inode), sizeof(struct nfs_fh));
> lock->caller = utsname()->nodename;
> lock->oh.data = req->a_owner;
> @@ -519,6 +518,7 @@ nlmclnt_lock(struct nlm_rqst *req, struct file_lock *fl)
>
> if (nsm_monitor(host) < 0)
> goto out;
> + req->a_args.state = nsm_local_state;
Hm. It looks like a_args.state is never used, except in ifdef'd-out
code in nlm4svc_proc_lock() and nlmsvc_proc_lock() ifdef'd out.
Something's wrong there. (Not your fault; but needs looking into.)
>
> fl->fl_flags |= FL_ACCESS;
> status = do_vfs_lock(fl);
> diff --git a/fs/lockd/mon.c b/fs/lockd/mon.c
> index 6d5d4a4..5017d50 100644
> --- a/fs/lockd/mon.c
> +++ b/fs/lockd/mon.c
> @@ -188,8 +188,12 @@ int nsm_monitor(const struct nlm_host *host)
> status = -EIO;
> if (status < 0)
> printk(KERN_NOTICE "lockd: cannot monitor %s\n", nsm->sm_name);
> - else
> + else {
> nsm->sm_monitored = 1;
> + nsm_local_state = res.state;
> + dprintk("lockd: nsm_monitor: NSM state is now %d\n",
> + nsm_local_state);
Could we make that a dprintk in the case where this changes nsm_local
state from something other than zero (nsm_lock_state && nsm_local_state
!= res.state)?
(Just to make sure no statd is returning inconsistent nsm_local_stats
here.)
> + }
> return status;
> }
--b.
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