On Thu, 2012-05-24 at 08:36 +0400, Stanislav Kinsbursky wrote:
> 23.05.2012 21:32, Trond Myklebust написал:
> > Ensure that a process that uses the nfs_client->cl_cons_state test
> > for whether the initialisation process is finished does not read
> > stale data.
> >
> > Signed-off-by: Trond Myklebust<Trond.Myklebust@xxxxxxxxxx>
> > ---
> > fs/nfs/client.c | 5 +++++
> > fs/nfs/idmap.c | 1 +
> > 2 files changed, 6 insertions(+), 0 deletions(-)
> >
> > diff --git a/fs/nfs/client.c b/fs/nfs/client.c
> > index e6070ea..4be85f9 100644
> > --- a/fs/nfs/client.c
> > +++ b/fs/nfs/client.c
> > @@ -456,6 +456,8 @@ static bool nfs4_cb_match_client(const struct sockaddr *addr,
> > clp->cl_cons_state == NFS_CS_SESSION_INITING))
> > return false;
> >
> > + smp_rmb();
> > +
> > /* Match the version and minorversion */
> > if (clp->rpc_ops->version != 4 ||
> > clp->cl_minorversion != minorversion)
> > @@ -587,6 +589,8 @@ found_client:
> > return ERR_PTR(error);
> > }
> >
> > + smp_rmb();
> > +
> > BUG_ON(clp->cl_cons_state != NFS_CS_READY);
> >
> > dprintk("--> nfs_get_client() = %p [share]\n", clp);
> > @@ -598,6 +602,7 @@ found_client:
> > */
> > void nfs_mark_client_ready(struct nfs_client *clp, int state)
> > {
> > + smp_wmb();
>
> BTW, why barrier is before assignment?
So that we write the initialisation changes to the struct nfs_client
before changing the value of clp->cl_cons_state. Otherwise, another
processor might see the change to clp->cl_cons_state before they see the
rest of the initialisation of clp.
Note that there is a second write barrier in the 'wake_up_all' call to
ensure that sleeping processes that are actually woken up will see the
change to clp->cl_cons_state.
> > clp->cl_cons_state = state;
> > wake_up_all(&nfs_client_active_wq);
> > }
> > diff --git a/fs/nfs/idmap.c b/fs/nfs/idmap.c
> > index 6ca949b..7d4e8dd 100644
> > --- a/fs/nfs/idmap.c
> > +++ b/fs/nfs/idmap.c
> > @@ -548,6 +548,7 @@ restart:
> > /* Skip nfs_clients that failed to initialise */
> > if (clp->cl_cons_state< 0)
> > continue;
> > + smp_rmb();
> > if (clp->rpc_ops !=&nfs_v4_clientops)
> > continue;
> > cl_dentry = clp->cl_idmap->idmap_pipe->dentry;
>
--
Trond Myklebust
Linux NFS client maintainer
NetApp
Trond.Myklebust@xxxxxxxxxx
www.netapp.com
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