nfs42: serialize LAYOUTSTATS calls of the same file

There is no need to report concurrently.
Reviewed-by: Jeff Layton <jeff.layton@primarydata.com>
Signed-off-by: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/nfs42proc.c

@@ -204,6 +204,9 @@ nfs42_layoutstat_release(void *calldata)
 		nfss->pnfs_curr_ld->cleanup_layoutstats(data);
 
 	pnfs_put_layout_hdr(NFS_I(data->args.inode)->layout);
+	smp_mb__before_atomic();
+	clear_bit(NFS_INO_LAYOUTSTATS, &NFS_I(data->args.inode)->flags);
+	smp_mb__after_atomic();
 	nfs_iput_and_deactive(data->inode);
 	kfree(data->args.devinfo);
 	kfree(data);

fs/nfs/pnfs.c

@@ -2257,6 +2257,7 @@ pnfs_report_layoutstat(struct inode *inode)
 {
 	struct pnfs_layoutdriver_type *ld = NFS_SERVER(inode)->pnfs_curr_ld;
 	struct nfs_server *server = NFS_SERVER(inode);
+	struct nfs_inode *nfsi = NFS_I(inode);
 	struct nfs42_layoutstat_data *data;
 	struct pnfs_layout_hdr *hdr;
 	int status = 0;
@@ -2264,6 +2265,9 @@ pnfs_report_layoutstat(struct inode *inode)
 	if (!pnfs_enabled_sb(server) || !ld->prepare_layoutstats)
 		goto out;
 
+	if (test_and_set_bit(NFS_INO_LAYOUTSTATS, &nfsi->flags))
+		goto out;
+
 	spin_lock(&inode->i_lock);
 	if (!NFS_I(inode)->layout) {
 		spin_unlock(&inode->i_lock);
@@ -2296,6 +2300,9 @@ pnfs_report_layoutstat(struct inode *inode)
 	kfree(data);
 out_put:
 	pnfs_put_layout_hdr(hdr);
+	smp_mb__before_atomic();
+	clear_bit(NFS_INO_LAYOUTSTATS, &nfsi->flags);
+	smp_mb__after_atomic();
 	goto out;
 }
 EXPORT_SYMBOL_GPL(pnfs_report_layoutstat);

include/linux/nfs_fs.h

@@ -219,6 +219,7 @@ struct nfs_inode {
 #define NFS_INO_COMMIT		(7)		/* inode is committing unstable writes */
 #define NFS_INO_LAYOUTCOMMIT	(9)		/* layoutcommit required */
 #define NFS_INO_LAYOUTCOMMITTING (10)		/* layoutcommit inflight */
+#define NFS_INO_LAYOUTSTATS	(11)		/* layoutstats inflight */
 
 static inline struct nfs_inode *NFS_I(const struct inode *inode)
 {