Re: [PATCH 1/3] nfsd: don't take nfsd_mutex twice when setting number of threads.

Jeff Layton
2009-06-11T17:52:57Z

On Thu, 28 May 2009 16:33:03 +1000
NeilBrown <neilb@suse.de> wrote:

> Currently when we right a number to 'threads' in nfsdfs,
> we take the nfsd_mutex, update the number of threads, then take the
> mutex again to read the number of threads.
>
> Mostly this isn't a big deal. However if we are write '0', and
> portmap happens to be dead, then we can get unpredictable behaviour.
> If the nfsd threads all got killed quickly and the last thread is
> waiting for portmap to respond, then the second time we take the mutex
> we will block waiting for the last thread.
> However if the nfsd threads didn't die quite that fast, then there
> will be no contention when we try to take the mutex again.
>
> Unpredictability isn't fun, and waiting for the last thread to exit is
> pointless, so avoid taking the lock twice.
> To achieve this, get nfsd_svc return a non-negative number of active
> threads when not returning a negative error.
>
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>
> fs/nfsd/nfsctl.c | 13 +++++++++----
> fs/nfsd/nfssvc.c | 2 ++
> 2 files changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index af16849..1ddd4f9 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -207,10 +207,14 @@ static struct file_operations pool_stats_operations = {
> static ssize_t write_svc(struct file *file, char *buf, size_t size)
> {
> struct nfsctl_svc *data;
> + int err;
> if (size < sizeof(*data))
> return -EINVAL;
> data = (struct nfsctl_svc*) buf;
> - return nfsd_svc(data->svc_port, data->svc_nthreads);
> + err = nfsd_svc(data->svc_port, data->svc_nthreads);
> + if (err < 0)
> + return err;
> + return 0;
> }
>
> /**
> @@ -692,10 +696,11 @@ static ssize_t write_threads(struct file *file, char *buf, size_t size)
> if (newthreads < 0)
> return -EINVAL;
> rv = nfsd_svc(NFS_PORT, newthreads);
> - if (rv)
> + if (rv < 0)
> return rv;
> - }
> - sprintf(buf, "%d\n", nfsd_nrthreads());
> + } else
> + rv = nfsd_nrthreads();
> + sprintf(buf, "%d\n", rv);
> return strlen(buf);
> }
>
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index cbba4a9..df6c59e 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -413,6 +413,8 @@ nfsd_svc(unsigned short port, int nrservs)
> goto failure;
>
> error = svc_set_num_threads(nfsd_serv, NULL, nrservs);
> + if (error == 0)
> + error = nfsd_serv->sv_nrthreads - 1;
^^^^
Why -1 here? I thought you wanted nfsd_svc to return the number of
threads?

Also, looks like Bruce's tree has changed a bit recently and I don't
think this patch will apply cleanly now. You may need to respin...

> failure:
> svc_destroy(nfsd_serv); /* Release server */
> out:
>
>
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--
Jeff Layton <jlayton@redhat.com>