Patch "SUNRPC: always treat sv_nrpools==1 as "not pooled"" has been added to the 5.10-stable tree

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This is a note to let you know that I've just added the patch titled

    SUNRPC: always treat sv_nrpools==1 as "not pooled"

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sunrpc-always-treat-sv_nrpools-1-as-not-pooled.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9e6a59ef833175cf1138349b250348bbb9f8131c
Author: NeilBrown <neilb@xxxxxxx>
Date:   Mon Nov 29 15:51:25 2021 +1100

    SUNRPC: always treat sv_nrpools==1 as "not pooled"
    
    [ Upstream commit 93aa619eb0b42eec2f3a9b4d9db41f5095390aec ]
    
    Currently 'pooled' services hold a reference on the pool_map, and
    'unpooled' services do not.
    svc_destroy() uses the presence of ->svo_function (via
    svc_serv_is_pooled()) to determine if the reference should be dropped.
    There is no direct correlation between being pooled and the use of
    svo_function, though in practice, lockd is the only non-pooled service,
    and the only one not to use svo_function.
    
    This is untidy and would cause problems if we changed lockd to use
    svc_set_num_threads(), which requires the use of ->svo_function.
    
    So change the test for "is the service pooled" to "is sv_nrpools > 1".
    
    This means that when svc_pool_map_get() returns 1, it must NOT take a
    reference to the pool.
    
    We discard svc_serv_is_pooled(), and test sv_nrpools directly.
    
    Signed-off-by: NeilBrown <neilb@xxxxxxx>
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index c681ac1c9d569..ceccd4ae5f797 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -35,8 +35,6 @@
 
 static void svc_unregister(const struct svc_serv *serv, struct net *net);
 
-#define svc_serv_is_pooled(serv)    ((serv)->sv_ops->svo_function)
-
 #define SVC_POOL_DEFAULT	SVC_POOL_GLOBAL
 
 /*
@@ -238,8 +236,10 @@ svc_pool_map_init_pernode(struct svc_pool_map *m)
 
 /*
  * Add a reference to the global map of cpus to pools (and
- * vice versa).  Initialise the map if we're the first user.
- * Returns the number of pools.
+ * vice versa) if pools are in use.
+ * Initialise the map if we're the first user.
+ * Returns the number of pools. If this is '1', no reference
+ * was taken.
  */
 static unsigned int
 svc_pool_map_get(void)
@@ -251,6 +251,7 @@ svc_pool_map_get(void)
 
 	if (m->count++) {
 		mutex_unlock(&svc_pool_map_mutex);
+		WARN_ON_ONCE(m->npools <= 1);
 		return m->npools;
 	}
 
@@ -266,29 +267,36 @@ svc_pool_map_get(void)
 		break;
 	}
 
-	if (npools < 0) {
+	if (npools <= 0) {
 		/* default, or memory allocation failure */
 		npools = 1;
 		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 m->npools;
+	return npools;
 }
 
 /*
- * Drop a reference to the global map of cpus to pools.
+ * Drop a reference to the global map of cpus to pools, if
+ * pools were in use, i.e. if npools > 1.
  * 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.
  */
 static void
-svc_pool_map_put(void)
+svc_pool_map_put(int npools)
 {
 	struct svc_pool_map *m = &svc_pool_map;
 
+	if (npools <= 1)
+		return;
 	mutex_lock(&svc_pool_map_mutex);
 
 	if (!--m->count) {
@@ -357,21 +365,18 @@ svc_pool_for_cpu(struct svc_serv *serv, int cpu)
 	struct svc_pool_map *m = &svc_pool_map;
 	unsigned int pidx = 0;
 
-	/*
-	 * An uninitialised map happens in a pure client when
-	 * lockd is brought up, so silently treat it the
-	 * same as SVC_POOL_GLOBAL.
-	 */
-	if (svc_serv_is_pooled(serv)) {
-		switch (m->mode) {
-		case SVC_POOL_PERCPU:
-			pidx = m->to_pool[cpu];
-			break;
-		case SVC_POOL_PERNODE:
-			pidx = m->to_pool[cpu_to_node(cpu)];
-			break;
-		}
+	if (serv->sv_nrpools <= 1)
+		return serv->sv_pools;
+
+	switch (m->mode) {
+	case SVC_POOL_PERCPU:
+		pidx = m->to_pool[cpu];
+		break;
+	case SVC_POOL_PERNODE:
+		pidx = m->to_pool[cpu_to_node(cpu)];
+		break;
 	}
+
 	return &serv->sv_pools[pidx % serv->sv_nrpools];
 }
 
@@ -524,7 +529,7 @@ svc_create_pooled(struct svc_program *prog, unsigned int bufsize,
 		goto out_err;
 	return serv;
 out_err:
-	svc_pool_map_put();
+	svc_pool_map_put(npools);
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(svc_create_pooled);
@@ -559,8 +564,7 @@ svc_destroy(struct kref *ref)
 
 	cache_clean_deferred(serv);
 
-	if (svc_serv_is_pooled(serv))
-		svc_pool_map_put();
+	svc_pool_map_put(serv->sv_nrpools);
 
 	kfree(serv->sv_pools);
 	kfree(serv);




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