nfsd: fix handling of cached open files in nfsd4_open codepath

Commit fb70bf12 ("NFSD: Instantiate a struct file when creating a
regular NFSv4 file") added the ability to cache an open fd over a
compound. There are a couple of problems with the way this currently
works:

It's racy, as a newly-created nfsd_file can end up with its PENDING bit
cleared while the nf is hashed, and the nf_file pointer is still zeroed
out. Other tasks can find it in this state and they expect to see a
valid nf_file, and can oops if nf_file is NULL.

Also, there is no guarantee that we'll end up creating a new nfsd_file
if one is already in the hash. If an extant entry is in the hash with a
valid nf_file, nfs4_get_vfs_file will clobber its nf_file pointer with
the value of op_file and the old nf_file will leak.

Fix both issues by making a new nfsd_file_acquirei_opened variant that
takes an optional file pointer. If one is present when this is called,
we'll take a new reference to it instead of trying to open the file. If
the nfsd_file already has a valid nf_file, we'll just ignore the
optional file and pass the nfsd_file back as-is.

Also rework the tracepoints a bit to allow for an "opened" variant and
don't try to avoid counting acquisitions in the case where we already
have a cached open file.

Fixes: fb70bf12 ("NFSD: Instantiate a struct file when creating a regular NFSv4 file")
Cc: Trond Myklebust <trondmy@hammerspace.com>
Reported-by: Stanislav Saner <ssaner@redhat.com>
Reported-and-Tested-by: Ruben Vestergaard <rubenv@drcmr.dk>
Reported-and-Tested-by: Torkil Svensgaard <torkil@drcmr.dk>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/filecache.c

@@ -1071,8 +1071,8 @@ nfsd_file_is_cached(struct inode *inode)
 
 static __be32
 nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
-		     unsigned int may_flags, struct nfsd_file **pnf,
-		     bool open, bool want_gc)
+		     unsigned int may_flags, struct file *file,
+		     struct nfsd_file **pnf, bool want_gc)
 {
 	struct nfsd_file_lookup_key key = {
 		.type	= NFSD_FILE_KEY_FULL,
@@ -1147,8 +1147,7 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	status = nfserrno(nfsd_open_break_lease(file_inode(nf->nf_file), may_flags));
 out:
 	if (status == nfs_ok) {
-		if (open)
-			this_cpu_inc(nfsd_file_acquisitions);
+		this_cpu_inc(nfsd_file_acquisitions);
 		*pnf = nf;
 	} else {
 		if (refcount_dec_and_test(&nf->nf_ref))
@@ -1158,20 +1157,23 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 out_status:
 	put_cred(key.cred);
-	if (open)
-		trace_nfsd_file_acquire(rqstp, key.inode, may_flags, nf, status);
+	trace_nfsd_file_acquire(rqstp, key.inode, may_flags, nf, status);
 	return status;
 
 open_file:
 	trace_nfsd_file_alloc(nf);
 	nf->nf_mark = nfsd_file_mark_find_or_create(nf, key.inode);
 	if (nf->nf_mark) {
-		if (open) {
+		if (file) {
+			get_file(file);
+			nf->nf_file = file;
+			status = nfs_ok;
+			trace_nfsd_file_opened(nf, status);
+		} else {
 			status = nfsd_open_verified(rqstp, fhp, may_flags,
 						    &nf->nf_file);
 			trace_nfsd_file_open(nf, status);
-		} else
-			status = nfs_ok;
+		}
 	} else
 		status = nfserr_jukebox;
 	/*
@@ -1207,7 +1209,7 @@ __be32
 nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		     unsigned int may_flags, struct nfsd_file **pnf)
 {
-	return nfsd_file_do_acquire(rqstp, fhp, may_flags, pnf, true, true);
+	return nfsd_file_do_acquire(rqstp, fhp, may_flags, NULL, pnf, true);
 }
 
 /**
@@ -1228,28 +1230,30 @@ __be32
 nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		  unsigned int may_flags, struct nfsd_file **pnf)
 {
-	return nfsd_file_do_acquire(rqstp, fhp, may_flags, pnf, true, false);
+	return nfsd_file_do_acquire(rqstp, fhp, may_flags, NULL, pnf, false);
 }
 
 /**
- * nfsd_file_create - Get a struct nfsd_file, do not open
+ * nfsd_file_acquire_opened - Get a struct nfsd_file using existing open file
  * @rqstp: the RPC transaction being executed
  * @fhp: the NFS filehandle of the file just created
  * @may_flags: NFSD_MAY_ settings for the file
+ * @file: cached, already-open file (may be NULL)
  * @pnf: OUT: new or found "struct nfsd_file" object
  *
- * The nfsd_file_object returned by this API is reference-counted
- * but not garbage-collected. The object is released immediately
- * one RCU grace period after the final nfsd_file_put().
+ * Acquire a nfsd_file object that is not GC'ed. If one doesn't already exist,
+ * and @file is non-NULL, use it to instantiate a new nfsd_file instead of
+ * opening a new one.
  *
  * Returns nfs_ok and sets @pnf on success; otherwise an nfsstat in
  * network byte order is returned.
  */
 __be32
-nfsd_file_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
-		 unsigned int may_flags, struct nfsd_file **pnf)
+nfsd_file_acquire_opened(struct svc_rqst *rqstp, struct svc_fh *fhp,
+			 unsigned int may_flags, struct file *file,
+			 struct nfsd_file **pnf)
 {
-	return nfsd_file_do_acquire(rqstp, fhp, may_flags, pnf, false, false);
+	return nfsd_file_do_acquire(rqstp, fhp, may_flags, file, pnf, false);
 }
 
 /*

fs/nfsd/filecache.h

@@ -60,7 +60,8 @@ __be32 nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		  unsigned int may_flags, struct nfsd_file **nfp);
 __be32 nfsd_file_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		  unsigned int may_flags, struct nfsd_file **nfp);
-__be32 nfsd_file_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
-		  unsigned int may_flags, struct nfsd_file **nfp);
+__be32 nfsd_file_acquire_opened(struct svc_rqst *rqstp, struct svc_fh *fhp,
+		  unsigned int may_flags, struct file *file,
+		  struct nfsd_file **nfp);
 int nfsd_file_cache_stats_show(struct seq_file *m, void *v);
 #endif /* _FS_NFSD_FILECACHE_H */

fs/nfsd/nfs4state.c

@@ -5262,18 +5262,10 @@ static __be32 nfs4_get_vfs_file(struct svc_rqst *rqstp, struct nfs4_file *fp,
 	if (!fp->fi_fds[oflag]) {
 		spin_unlock(&fp->fi_lock);
 
-		if (!open->op_filp) {
-			status = nfsd_file_acquire(rqstp, cur_fh, access, &nf);
-			if (status != nfs_ok)
-				goto out_put_access;
-		} else {
-			status = nfsd_file_create(rqstp, cur_fh, access, &nf);
-			if (status != nfs_ok)
-				goto out_put_access;
-			nf->nf_file = open->op_filp;
-			open->op_filp = NULL;
-			trace_nfsd_file_create(rqstp, access, nf);
-		}
+		status = nfsd_file_acquire_opened(rqstp, cur_fh, access,
+						  open->op_filp, &nf);
+		if (status != nfs_ok)
+			goto out_put_access;
 
 		spin_lock(&fp->fi_lock);
 		if (!fp->fi_fds[oflag]) {

fs/nfsd/trace.h

@@ -981,43 +981,6 @@ TRACE_EVENT(nfsd_file_acquire,
 	)
 );
 
-TRACE_EVENT(nfsd_file_create,
-	TP_PROTO(
-		const struct svc_rqst *rqstp,
-		unsigned int may_flags,
-		const struct nfsd_file *nf
-	),
-
-	TP_ARGS(rqstp, may_flags, nf),
-
-	TP_STRUCT__entry(
-		__field(const void *, nf_inode)
-		__field(const void *, nf_file)
-		__field(unsigned long, may_flags)
-		__field(unsigned long, nf_flags)
-		__field(unsigned long, nf_may)
-		__field(unsigned int, nf_ref)
-		__field(u32, xid)
-	),
-
-	TP_fast_assign(
-		__entry->nf_inode = nf->nf_inode;
-		__entry->nf_file = nf->nf_file;
-		__entry->may_flags = may_flags;
-		__entry->nf_flags = nf->nf_flags;
-		__entry->nf_may = nf->nf_may;
-		__entry->nf_ref = refcount_read(&nf->nf_ref);
-		__entry->xid = be32_to_cpu(rqstp->rq_xid);
-	),
-
-	TP_printk("xid=0x%x inode=%p may_flags=%s ref=%u nf_flags=%s nf_may=%s nf_file=%p",
-		__entry->xid, __entry->nf_inode,
-		show_nfsd_may_flags(__entry->may_flags),
-		__entry->nf_ref, show_nf_flags(__entry->nf_flags),
-		show_nfsd_may_flags(__entry->nf_may), __entry->nf_file
-	)
-);
-
 TRACE_EVENT(nfsd_file_insert_err,
 	TP_PROTO(
 		const struct svc_rqst *rqstp,
@@ -1079,8 +1042,8 @@ TRACE_EVENT(nfsd_file_cons_err,
 	)
 );
 
-TRACE_EVENT(nfsd_file_open,
-	TP_PROTO(struct nfsd_file *nf, __be32 status),
+DECLARE_EVENT_CLASS(nfsd_file_open_class,
+	TP_PROTO(const struct nfsd_file *nf, __be32 status),
 	TP_ARGS(nf, status),
 	TP_STRUCT__entry(
 		__field(void *, nf_inode)	/* cannot be dereferenced */
@@ -1104,6 +1067,17 @@ TRACE_EVENT(nfsd_file_open,
 		__entry->nf_file)
 )
 
+#define DEFINE_NFSD_FILE_OPEN_EVENT(name)					\
+DEFINE_EVENT(nfsd_file_open_class, name,					\
+	TP_PROTO(							\
+		const struct nfsd_file *nf,				\
+		__be32 status						\
+	),								\
+	TP_ARGS(nf, status))
+
+DEFINE_NFSD_FILE_OPEN_EVENT(nfsd_file_open);
+DEFINE_NFSD_FILE_OPEN_EVENT(nfsd_file_opened);
+
 TRACE_EVENT(nfsd_file_is_cached,
 	TP_PROTO(
 		const struct inode *inode,