NFS: struct nfs_commit_info.lock must always point to inode->i_lock

Commit 411a99adffb4f (nfs: clear_request_commit while holding i_lock)
assumes that the nfs_commit_info always points to the inode->i_lock.
For historical reasons, that is not the case for O_DIRECT writes.

Cc: Weston Andros Adamson <dros@primarydata.com>
Fixes: 411a99adffb4f ("nfs: clear_request_commit while holding i_lock")
Cc: stable@vger.kernel.org # 3.17.x
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/direct.c

@@ -283,7 +283,7 @@ static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
 void nfs_init_cinfo_from_dreq(struct nfs_commit_info *cinfo,
 			      struct nfs_direct_req *dreq)
 {
-	cinfo->lock = &dreq->lock;
+	cinfo->lock = &dreq->inode->i_lock;
 	cinfo->mds = &dreq->mds_cinfo;
 	cinfo->ds = &dreq->ds_cinfo;
 	cinfo->dreq = dreq;

include/linux/nfs_xdr.h

@@ -1351,7 +1351,7 @@ struct nfs_commit_completion_ops {
 };
 
 struct nfs_commit_info {
-	spinlock_t			*lock;
+	spinlock_t			*lock;	/* inode->i_lock */
 	struct nfs_mds_commit_info	*mds;
 	struct pnfs_ds_commit_info	*ds;
 	struct nfs_direct_req		*dreq;	/* O_DIRECT request */