linux-kernel - [PATCH 1/3] sunrpc: fix up the special handling of sv

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Message-Id: <20240604-nfsd-next-v1-1-8df686ae61de@kernel.org>
Date: Tue, 04 Jun 2024 17:07:54 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Chuck Lever <chuck.lever@...cle.com>, Neil Brown <neilb@...e.de>, 
 Olga Kornievskaia <kolga@...app.com>, Dai Ngo <Dai.Ngo@...cle.com>, 
 Tom Talpey <tom@...pey.com>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>
Cc: Trond Myklebust <trond.myklebust@...merspace.com>, 
 Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org, 
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
 Jeff Layton <jlayton@...nel.org>
Subject: [PATCH 1/3] sunrpc: fix up the special handling of sv_nrpools == 1

Only pooled services take a reference to the svc_pool_map. The sunrpc
code has always used the sv_nrpools value to detect whether the service
is pooled.

The problem there is that nfsd is a pooled service, but when it's
running in "global" pool_mode, it doesn't take a reference to the pool
map because it has a sv_nrpools value of 1. This means that we have
two separate codepaths for starting the server, depending on whether
it's pooled or not.

Fix this by adding a new flag to the svc_serv, that indicates whether
the serv is pooled. With this we can have the nfsd service
unconditionally take a reference, regardless of pool_mode.

Ideally we should prevent anyone from changing the pool mode while the
server is running, and nfsd does this if the server is in percpu or
pernode mode. Previously, you could change the pool_mode even if there
were nfsd's already running in "global" mode. This fixes that problem as
well.

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 include/linux/sunrpc/svc.h |  1 +
 net/sunrpc/svc.c           | 26 +++++++-------------------
 2 files changed, 8 insertions(+), 19 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 23617da0e565..d0433e1642b3 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -85,6 +85,7 @@ struct svc_serv {
 	char *			sv_name;	/* service name */

 	unsigned int		sv_nrpools;	/* number of thread pools */
+	bool			sv_is_pooled;	/* is this a pooled service? */
 	struct svc_pool *	sv_pools;	/* array of thread pools */
 	int			(*sv_threadfn)(void *data);

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 2b4b1276d4e8..f80d94cbb8b1 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -250,10 +250,8 @@ svc_pool_map_get(void)
 	int npools = -1;

 	mutex_lock(&svc_pool_map_mutex);
-
 	if (m->count++) {
 		mutex_unlock(&svc_pool_map_mutex);
-		WARN_ON_ONCE(m->npools <= 1);
 		return m->npools;
 	}

@@ -275,32 +273,21 @@ svc_pool_map_get(void)
 		m->mode = SVC_POOL_GLOBAL;
 	}
 	m->npools = npools;
-
-	if (npools == 1)
-		/* service is unpooled, so doesn't hold a reference */
-		m->count--;
-
 	mutex_unlock(&svc_pool_map_mutex);
 	return npools;
 }

 /*
- * Drop a reference to the global map of cpus to pools, if
- * pools were in use, i.e. if npools > 1.
+ * Drop a reference to the global map of cpus to pools.
  * When the last reference is dropped, the map data is
- * freed; this allows the sysadmin to change the pool
- * mode using the pool_mode module option without
- * rebooting or re-loading sunrpc.ko.
+ * freed; this allows the sysadmin to change the pool.
  */
 static void
-svc_pool_map_put(int npools)
+svc_pool_map_put(void)
 {
 	struct svc_pool_map *m = &svc_pool_map;

-	if (npools <= 1)
-		return;
 	mutex_lock(&svc_pool_map_mutex);
-
 	if (!--m->count) {
 		kfree(m->to_pool);
 		m->to_pool = NULL;
@@ -308,7 +295,6 @@ svc_pool_map_put(int npools)
 		m->pool_to = NULL;
 		m->npools = 0;
 	}
-
 	mutex_unlock(&svc_pool_map_mutex);
 }

@@ -553,9 +539,10 @@ struct svc_serv *svc_create_pooled(struct svc_program *prog,
 	serv = __svc_create(prog, stats, bufsize, npools, threadfn);
 	if (!serv)
 		goto out_err;
+	serv->sv_is_pooled = true;
 	return serv;
 out_err:
-	svc_pool_map_put(npools);
+	svc_pool_map_put();
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(svc_create_pooled);
@@ -585,7 +572,8 @@ svc_destroy(struct svc_serv **servp)

 	cache_clean_deferred(serv);

-	svc_pool_map_put(serv->sv_nrpools);
+	if (serv->sv_is_pooled)
+		svc_pool_map_put();

 	for (i = 0; i < serv->sv_nrpools; i++) {
 		struct svc_pool *pool = &serv->sv_pools[i];

-- 
2.45.1