[PATCH v3 03/17] nfsd: replace fh_fill_both_attrs() with fh_fill_post_noop()

[NeilBrown <neilb@ownmail.net>]

From: NeilBrown <neil@brown.name>

fh_fill_both_attrs() is only needed for open/create and is used in the
case when the target already existed so no creating happens.

As part of refactoring this code it is changed to call
fh_fill_pre_attrs() once early on (so errors only need to be caught in
one place) and then to use a new fh_fill_post_noop() when it is
determined that no creation happened.

fh_fill_pre_attrs() now stores the attrs (which it had to get all of
anyway)_ in ->fh_post_attr.  fh_fill_post_noop() simply marks them as
valid.  fh_fill_post_attrs() replaces them.

This change involves moving fh_fill_pre_attrs() out of the inode_lock on
the directory.  This means that we cannot provide "atomic" wcc data so a
new fh_fill_pre_attrs_unlocked() is provided which marks the attrs as
non-atomic.

This is unfortunate but inevitable if we are ever to allow concurrent
updates in a directory (which can significantly improve performance in
some cases).  To get atomic pre/post attributes we will need to be able
to ask the fs to provide them, or to request a lease on the directory
for the duration of an operation.

Note that we haven't provided pre/post attrs on WRITE requests for a
long time for exactly this reason - we cannot lock the file to get them.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/nfsd/nfs4proc.c | 23 +++++++---------
 fs/nfsd/nfsfh.c    | 69 +++++++++++++++++++++++-----------------------
 fs/nfsd/nfsfh.h    | 14 +++++++++-
 3 files changed, 57 insertions(+), 49 deletions(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 9a8c1e37cc0f..3e5c1fdde57b 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -285,8 +285,7 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 				if (status == nfs_ok)
 					status = fh_compose(resfhp, exp,
 							    child, fhp);
-				if (status == nfs_ok)
-					status = fh_fill_both_attrs(fhp);
+				fh_fill_post_noop(fhp);
 				open->op_truncate =
 					(iap->ia_valid & ATTR_SIZE) &&
 					!iap->ia_size;
@@ -357,9 +356,7 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		/* NFSv4 protocol requires change attributes even though
 		 * no change happened.
 		 */
-		status = fh_fill_both_attrs(fhp);
-		if (status != nfs_ok)
-			goto out;
+		fh_fill_post_noop(fhp);
 
 		status = fh_compose(resfhp, fhp->fh_export, child, fhp);
 		if (status != nfs_ok)
@@ -406,9 +403,6 @@ nfsd4_create_file(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (!IS_POSIXACL(inode))
 		iap->ia_mode &= ~current_umask();
 
-	status = fh_fill_pre_attrs(fhp);
-	if (status != nfs_ok)
-		goto out;
 	status = nfsd4_vfs_create(fhp, &child, open);
 	if (status != nfs_ok)
 		goto out;
@@ -494,6 +488,9 @@ do_open_lookup(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, stru
 	fh_init(*resfh, NFS4_FHSIZE);
 	open->op_truncate = false;
 
+	status = fh_fill_pre_attrs_unlocked(current_fh);
+	if (status)
+		goto out;
 	if (open->op_create) {
 		/* FIXME: check session persistence and pnfs flags.
 		 * The nfsv4.1 spec requires the following semantics:
@@ -525,11 +522,11 @@ do_open_lookup(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, stru
 	} else {
 		status = nfsd_lookup(rqstp, current_fh,
 				     open->op_fname, open->op_fnamelen, *resfh);
-		if (status == nfs_ok)
-			/* NFSv4 protocol requires change attributes even though
-			 * no change happened.
-			 */
-			status = fh_fill_both_attrs(current_fh);
+		/*
+		 * NFSv4 protocol requires change attributes even though
+		 * no change happened.
+		 */
+		fh_fill_post_noop(current_fh);
 	}
 	if (status)
 		goto out;
diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index 8b1a95e1d058..26980bbb195f 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -780,34 +780,53 @@ __be32 fh_getattr(const struct svc_fh *fhp, struct kstat *stat)
 				    AT_STATX_SYNC_AS_STAT));
 }
 
-/**
- * fh_fill_pre_attrs - Fill in pre-op attributes
- * @fhp: file handle to be updated
- *
- */
-__be32 __must_check fh_fill_pre_attrs(struct svc_fh *fhp)
+static __be32 __must_check __fh_fill_pre_attrs(struct svc_fh *fhp)
 {
 	bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
-	struct kstat stat;
 	__be32 err;
 
 	if (fhp->fh_no_wcc || fhp->fh_pre_saved)
 		return nfs_ok;
 
-	err = fh_getattr(fhp, &stat);
+	err = fh_getattr(fhp, &fhp->fh_post_attr);
 	if (err)
 		return err;
 
 	if (v4)
-		fhp->fh_pre_change = nfsd4_change_attribute(&stat);
+		fhp->fh_pre_change = fhp->fh_post_change =
+			nfsd4_change_attribute(&fhp->fh_post_attr);
 
-	fhp->fh_pre_mtime = stat.mtime;
-	fhp->fh_pre_ctime = stat.ctime;
-	fhp->fh_pre_size  = stat.size;
+	fhp->fh_pre_mtime = fhp->fh_post_attr.mtime;
+	fhp->fh_pre_ctime = fhp->fh_post_attr.ctime;
+	fhp->fh_pre_size  = fhp->fh_post_attr.size;
 	fhp->fh_pre_saved = true;
 	return nfs_ok;
 }
 
+/**
+ * fh_fill_pre_attrs - Fill in pre-op attributes
+ * @fhp: file handle to be updated
+ *
+ * Post-op attrs are filled and pre-op attrs are copied
+ * from there.  The post-op attrs can later be replaced by
+ * fh_fill_post_attrs() or activated by fh_fill_post_noop().
+ *
+ * The inode must be locked.
+ *
+ * Returns: error from vfs_getattr() which must be checked.
+ */
+__be32 __must_check fh_fill_pre_attrs(struct svc_fh *fhp)
+{
+	lockdep_assert_held_write(&fhp->fh_dentry->d_inode->i_rwsem);
+	return __fh_fill_pre_attrs(fhp);
+}
+
+__be32 __must_check fh_fill_pre_attrs_unlocked(struct svc_fh *fhp)
+{
+	fhp->fh_no_atomic_attr = true;
+	return __fh_fill_pre_attrs(fhp);
+}
+
 /**
  * fh_fill_post_attrs - Fill in post-op attributes
  * @fhp: file handle to be updated
@@ -824,6 +843,9 @@ __be32 fh_fill_post_attrs(struct svc_fh *fhp)
 	if (fhp->fh_post_saved)
 		printk("nfsd: inode locked twice during operation.\n");
 
+	if (!fhp->fh_no_atomic_attr)
+		lockdep_assert_held_write(&fhp->fh_dentry->d_inode->i_rwsem);
+
 	err = fh_getattr(fhp, &fhp->fh_post_attr);
 	if (err)
 		return err;
@@ -835,29 +857,6 @@ __be32 fh_fill_post_attrs(struct svc_fh *fhp)
 	return nfs_ok;
 }
 
-/**
- * fh_fill_both_attrs - Fill pre-op and post-op attributes
- * @fhp: file handle to be updated
- *
- * This is used when the directory wasn't changed, but wcc attributes
- * are needed anyway.
- */
-__be32 __must_check fh_fill_both_attrs(struct svc_fh *fhp)
-{
-	__be32 err;
-
-	err = fh_fill_post_attrs(fhp);
-	if (err)
-		return err;
-
-	fhp->fh_pre_change = fhp->fh_post_change;
-	fhp->fh_pre_mtime = fhp->fh_post_attr.mtime;
-	fhp->fh_pre_ctime = fhp->fh_post_attr.ctime;
-	fhp->fh_pre_size = fhp->fh_post_attr.size;
-	fhp->fh_pre_saved = true;
-	return nfs_ok;
-}
-
 /*
  * Release a file handle.
  */
diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
index cdeb5eea65a8..ab15b59ac7b3 100644
--- a/fs/nfsd/nfsfh.h
+++ b/fs/nfsd/nfsfh.h
@@ -337,6 +337,18 @@ static inline void fh_clear_pre_post_attrs(struct svc_fh *fhp)
 
 u64 nfsd4_change_attribute(const struct kstat *stat);
 __be32 __must_check fh_fill_pre_attrs(struct svc_fh *fhp);
+__be32 __must_check fh_fill_pre_attrs_unlocked(struct svc_fh *fhp);
 __be32 fh_fill_post_attrs(struct svc_fh *fhp);
-__be32 __must_check fh_fill_both_attrs(struct svc_fh *fhp);
+
+/**
+ * fh_fill_post_noop - Copy pre attrs to post attrs
+ * @fhp: file handle to be updated
+ *
+ * This is used when the directory wasn't changed, but wcc attributes
+ * are needed anyway.
+ */
+static inline void fh_fill_post_noop(struct svc_fh *fhp)
+{
+	fhp->fh_post_saved = true;
+}
 #endif /* _LINUX_NFSD_NFSFH_H */
-- 
2.50.0.107.gf914562f5916.dirty