NFSv4.1: Fix pnfs_put_lseg races

pnfs_layoutreturn_free_lseg_async() can also race with inode put in
the general case. We can now fix this, and also simplify the code.

Cc: Peng Tao <tao.peng@primarydata.com>
Signed-off-by: NTrond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/pnfs.c

@@ -361,14 +361,9 @@ pnfs_layout_need_return(struct pnfs_layout_hdr *lo,
 	return true;
 }
 
-static void pnfs_layoutreturn_free_lseg(struct work_struct *work)
+static void pnfs_layoutreturn_before_put_lseg(struct pnfs_layout_segment *lseg,
+		struct pnfs_layout_hdr *lo, struct inode *inode)
 {
-	struct pnfs_layout_segment *lseg;
-	struct pnfs_layout_hdr *lo;
-	struct inode *inode;
-
-	lseg = container_of(work, struct pnfs_layout_segment, pls_work);
-	WARN_ON(atomic_read(&lseg->pls_refcount));
 	lo = lseg->pls_layout;
 	inode = lo->plh_inode;
 
@@ -383,24 +378,12 @@ static void pnfs_layoutreturn_free_lseg(struct work_struct *work)
 		lo->plh_block_lgets++;
 		lo->plh_return_iomode = 0;
 		spin_unlock(&inode->i_lock);
+		pnfs_get_layout_hdr(lo);
 
-		pnfs_send_layoutreturn(lo, stateid, iomode, true);
-		spin_lock(&inode->i_lock);
+		/* Send an async layoutreturn so we dont deadlock */
+		pnfs_send_layoutreturn(lo, stateid, iomode, false);
 	} else
-		/* match pnfs_get_layout_hdr #2 in pnfs_put_lseg */
-		pnfs_put_layout_hdr(lo);
-	pnfs_layout_remove_lseg(lo, lseg);
-	spin_unlock(&inode->i_lock);
-	pnfs_free_lseg(lseg);
-	/* match pnfs_get_layout_hdr #1 in pnfs_put_lseg */
-	pnfs_put_layout_hdr(lo);
-}
-
-static void
-pnfs_layoutreturn_free_lseg_async(struct pnfs_layout_segment *lseg)
-{
-	INIT_WORK(&lseg->pls_work, pnfs_layoutreturn_free_lseg);
-	queue_work(nfsiod_workqueue, &lseg->pls_work);
+		spin_unlock(&inode->i_lock);
 }
 
 void
@@ -415,21 +398,23 @@ pnfs_put_lseg(struct pnfs_layout_segment *lseg)
 	dprintk("%s: lseg %p ref %d valid %d\n", __func__, lseg,
 		atomic_read(&lseg->pls_refcount),
 		test_bit(NFS_LSEG_VALID, &lseg->pls_flags));
+
+	/* Handle the case where refcount != 1 */
+	if (atomic_add_unless(&lseg->pls_refcount, -1, 1))
+		return;
+
 	lo = lseg->pls_layout;
 	inode = lo->plh_inode;
+	/* Do we need a layoutreturn? */
+	if (test_bit(NFS_LSEG_LAYOUTRETURN, &lseg->pls_flags))
+		pnfs_layoutreturn_before_put_lseg(lseg, lo, inode);
+
 	if (atomic_dec_and_lock(&lseg->pls_refcount, &inode->i_lock)) {
 		pnfs_get_layout_hdr(lo);
-		if (pnfs_layout_need_return(lo, lseg)) {
-			spin_unlock(&inode->i_lock);
-			/* hdr reference dropped in nfs4_layoutreturn_release */
-			pnfs_get_layout_hdr(lo);
-			pnfs_layoutreturn_free_lseg_async(lseg);
-		} else {
-			pnfs_layout_remove_lseg(lo, lseg);
-			spin_unlock(&inode->i_lock);
-			pnfs_free_lseg(lseg);
-			pnfs_put_layout_hdr(lo);
-		}
+		pnfs_layout_remove_lseg(lo, lseg);
+		spin_unlock(&inode->i_lock);
+		pnfs_free_lseg(lseg);
+		pnfs_put_layout_hdr(lo);
 	}
 }
 EXPORT_SYMBOL_GPL(pnfs_put_lseg);