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Subject: [PATCH RFC 2/9] nfsd: rework hashtable handling in
 nfsd_do_file_acquire
From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org
Date:   Wed, 05 Oct 2022 10:55:48 -0400
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From: Jeff Layton <jlayton@kernel.org>

nfsd_file is RCU-freed, so we need to hold the rcu_read_lock long enough
to get a reference after finding it in the hash. Take the
rcu_read_lock() and call rhashtable_lookup directly.

Switch to using rhashtable_lookup_insert_key as well, and use the usual
retry mechanism if we hit an -EEXIST. Rename the "retry" bool to
open_retry, and eliminiate the insert_err goto target.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/filecache.c |   52 ++++++++++++++++++++++-----------------------------
 1 file changed, 22 insertions(+), 30 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 844c41832d50..a2adfc247648 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -1042,9 +1042,10 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		.need	= may_flags & NFSD_FILE_MAY_MASK,
 		.net	= SVC_NET(rqstp),
 	};
-	struct nfsd_file *nf, *new;
-	bool retry = true;
+	bool open_retry = true;
+	struct nfsd_file *nf;
 	__be32 status;
+	int ret;
 
 	status = fh_verify(rqstp, fhp, S_IFREG,
 				may_flags|NFSD_MAY_OWNER_OVERRIDE);
@@ -1054,35 +1055,33 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	key.cred = get_current_cred();
 
 retry:
-	/* Avoid allocation if the item is already in cache */
-	nf = rhashtable_lookup_fast(&nfsd_file_rhash_tbl, &key,
-				    nfsd_file_rhash_params);
+	rcu_read_lock();
+	nf = rhashtable_lookup(&nfsd_file_rhash_tbl, &key,
+			       nfsd_file_rhash_params);
 	if (nf)
 		nf = nfsd_file_get(nf);
+	rcu_read_unlock();
 	if (nf)
 		goto wait_for_construction;
 
-	new = nfsd_file_alloc(&key, may_flags);
-	if (!new) {
+	nf = nfsd_file_alloc(&key, may_flags);
+	if (!nf) {
 		status = nfserr_jukebox;
 		goto out_status;
 	}
 
-	nf = rhashtable_lookup_get_insert_key(&nfsd_file_rhash_tbl,
-					      &key, &new->nf_rhash,
-					      nfsd_file_rhash_params);
-	if (!nf) {
-		nf = new;
-		goto open_file;
-	}
-	if (IS_ERR(nf))
-		goto insert_err;
-	nf = nfsd_file_get(nf);
-	if (nf == NULL) {
-		nf = new;
+	ret = rhashtable_lookup_insert_key(&nfsd_file_rhash_tbl,
+					   &key, &nf->nf_rhash,
+					   nfsd_file_rhash_params);
+	if (likely(ret == 0))
 		goto open_file;
-	}
-	nfsd_file_slab_free(&new->nf_rcu);
+
+	nfsd_file_slab_free(&nf->nf_rcu);
+	if (ret == -EEXIST)
+		goto retry;
+	trace_nfsd_file_insert_err(rqstp, key.inode, may_flags, ret);
+	status = nfserr_jukebox;
+	goto out_status;
 
 wait_for_construction:
 	wait_on_bit(&nf->nf_flags, NFSD_FILE_PENDING, TASK_UNINTERRUPTIBLE);
@@ -1090,11 +1089,11 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	/* Did construction of this file fail? */
 	if (!test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
 		trace_nfsd_file_cons_err(rqstp, key.inode, may_flags, nf);
-		if (!retry) {
+		if (!open_retry) {
 			status = nfserr_jukebox;
 			goto out;
 		}
-		retry = false;
+		open_retry = false;
 		nfsd_file_put_noref(nf);
 		goto retry;
 	}
@@ -1142,13 +1141,6 @@ nfsd_file_do_acquire(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	smp_mb__after_atomic();
 	wake_up_bit(&nf->nf_flags, NFSD_FILE_PENDING);
 	goto out;
-
-insert_err:
-	nfsd_file_slab_free(&new->nf_rcu);
-	trace_nfsd_file_insert_err(rqstp, key.inode, may_flags, PTR_ERR(nf));
-	nf = NULL;
-	status = nfserr_jukebox;
-	goto out_status;
 }
 
 /**