On 2013-10-10 15:47, Nadav Shemer wrote:
> Some client_expire operations (pnfs_expire_client) may release the state
> lock. To prevent two threads from concurrently expiring the same client,
> the client is unhashed before any other operation
>
> Signed-off-by: Nadav Shemer <nadav@xxxxxxxxxxxxxxx>
> ---
> Related to the recent patchset from Benny Halevy, expire_client releases the state lock (expire_client->destroy_client->pnfs_expire_client).
> A different thread processing a SET_CLIENTID/EXCHANGE_ID/etc. might find the client on the confirmed/unconfirmed hash table and also call expire_client on it.
>
> To correct this, I reshuffled destroy_client to remove the client from hash tables first thing, before the state lock may be released
>
> Benny: my previous version of this patch had some plays with reference counts (taking a reference for the duration of the destroy).
> In the current version of the tree, destroy_client assumes cl_refcount==0 and is the only caller of free_client besides create_client. So I dropped it
OK.
In my state lock elimination branch this hunk is factored out and done under a spin lock
while the heavy lifting of managing the tracking record will be done under a mutex.
Benny
>
> fs/nfsd/nfs4state.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index b4a28ef..d42434b 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1154,57 +1154,60 @@ unhash_client_locked(struct nfs4_client *clp)
> list_del(&clp->cl_lru);
> spin_lock(&clp->cl_lock);
> list_for_each_entry(ses, &clp->cl_sessions, se_perclnt)
> list_del_init(&ses->se_hash);
> spin_unlock(&clp->cl_lock);
> }
>
> static void
> destroy_client(struct nfs4_client *clp)
> {
> struct nfs4_openowner *oo;
> struct nfs4_delegation *dp;
> struct list_head reaplist;
> struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
>
> + list_del(&clp->cl_idhash);
> + if (test_bit(NFSD4_CLIENT_CONFIRMED, &clp->cl_flags))
> + rb_erase(&clp->cl_namenode, &nn->conf_name_tree);
> + else
> + rb_erase(&clp->cl_namenode, &nn->unconf_name_tree);
> + spin_lock(&nn->client_lock);
> + unhash_client_locked(clp);
> + spin_unlock(&nn->client_lock);
> +
> INIT_LIST_HEAD(&reaplist);
> spin_lock(&recall_lock);
> while (!list_empty(&clp->cl_delegations)) {
> dp = list_entry(clp->cl_delegations.next, struct nfs4_delegation, dl_perclnt);
> list_del_init(&dp->dl_perclnt);
> list_move(&dp->dl_recall_lru, &reaplist);
> }
> spin_unlock(&recall_lock);
> while (!list_empty(&reaplist)) {
> dp = list_entry(reaplist.next, struct nfs4_delegation, dl_recall_lru);
> destroy_delegation(dp);
> }
> while (!list_empty(&clp->cl_openowners)) {
> oo = list_entry(clp->cl_openowners.next, struct nfs4_openowner, oo_perclient);
> release_openowner(oo);
> }
> pnfs_expire_client(clp);
> nfsd4_shutdown_callback(clp);
> if (clp->cl_cb_conn.cb_xprt)
> svc_xprt_put(clp->cl_cb_conn.cb_xprt);
> - list_del(&clp->cl_idhash);
> - if (test_bit(NFSD4_CLIENT_CONFIRMED, &clp->cl_flags))
> - rb_erase(&clp->cl_namenode, &nn->conf_name_tree);
> - else
> - rb_erase(&clp->cl_namenode, &nn->unconf_name_tree);
> spin_lock(&nn->client_lock);
> - unhash_client_locked(clp);
> WARN_ON_ONCE(atomic_read(&clp->cl_refcount));
> free_client(clp);
> spin_unlock(&nn->client_lock);
> }
>
> static void expire_client(struct nfs4_client *clp)
> {
> nfsd4_client_record_remove(clp);
> destroy_client(clp);
> }
>
> static void copy_verf(struct nfs4_client *target, nfs4_verifier *source)
> {
> memcpy(target->cl_verifier.data, source->data,
> sizeof(target->cl_verifier.data));
>
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