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Subject: [PATCH 09/14] SUNRPC: change how svc threads are asked to exit.
From:   NeilBrown <neilb@suse.de>
To:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     linux-nfs@vger.kernel.org
Date:   Tue, 18 Jul 2023 16:38:08 +1000
Message-ID: <168966228865.11075.10638610963240650169.stgit@noble.brown>
In-Reply-To: <168966227838.11075.2974227708495338626.stgit@noble.brown>
References: <168966227838.11075.2974227708495338626.stgit@noble.brown>
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svc threads are currently stopped using kthread_stop().  This requires
identifying a specific thread.  However we don't care which thread
stops, just as long as one does.

So instead, set a flag in the svc_pool to say that a thread needs to
die, and have each thread check this flag instead of calling
kthread_should_stop().  The first to find it clear the flag and moves
towards shutting down.

This removes an explicit dependency on sp_all_threads which will make a
future patch simpler.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/lockd/svc.c                |    4 ++--
 fs/lockd/svclock.c            |    4 ++--
 fs/nfs/callback.c             |    2 +-
 fs/nfsd/nfs4proc.c            |    8 +++++---
 fs/nfsd/nfssvc.c              |    2 +-
 include/linux/lockd/lockd.h   |    2 +-
 include/linux/sunrpc/svc.h    |   22 +++++++++++++++++++++-
 include/trace/events/sunrpc.h |    5 +++--
 net/sunrpc/svc.c              |   39 +++++++++++++++++----------------------
 net/sunrpc/svc_xprt.c         |    8 +++-----
 10 files changed, 56 insertions(+), 40 deletions(-)

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 4f55cd42c2e6..30543edd2309 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -134,12 +134,12 @@ lockd(void *vrqstp)
 	 * The main request loop. We don't terminate until the last
 	 * NFS mount or NFS daemon has gone away.
 	 */
-	while (!kthread_should_stop()) {
+	while (!svc_thread_should_stop(rqstp)) {
 
 		/* update sv_maxconn if it has changed */
 		rqstp->rq_server->sv_maxconn = nlm_max_connections;
 
-		nlmsvc_retry_blocked();
+		nlmsvc_retry_blocked(rqstp);
 
 		/*
 		 * Find any work to do, such as a socket with data available,
diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 3d7bd5c04b36..fd399c9bea5c 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -1009,13 +1009,13 @@ retry_deferred_block(struct nlm_block *block)
  * be retransmitted.
  */
 void
-nlmsvc_retry_blocked(void)
+nlmsvc_retry_blocked(struct svc_rqst *rqstp)
 {
 	unsigned long	timeout = MAX_SCHEDULE_TIMEOUT;
 	struct nlm_block *block;
 
 	spin_lock(&nlm_blocked_lock);
-	while (!list_empty(&nlm_blocked) && !kthread_should_stop()) {
+	while (!list_empty(&nlm_blocked) && !svc_thread_should_stop(rqstp)) {
 		block = list_entry(nlm_blocked.next, struct nlm_block, b_list);
 
 		if (block->b_when == NLM_NEVER)
diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 660cec36c45c..c58ec2e66aaf 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -78,7 +78,7 @@ nfs4_callback_svc(void *vrqstp)
 
 	set_freezable();
 
-	while (!kthread_should_stop()) {
+	while (!svc_thread_should_stop(rqstp)) {
 		/*
 		 * Listen for a request on the socket
 		 */
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 157488290676..66024ed06181 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1306,7 +1306,8 @@ extern void nfs_sb_deactive(struct super_block *sb);
  * setup a work entry in the ssc delayed unmount list.
  */
 static __be32 nfsd4_ssc_setup_dul(struct nfsd_net *nn, char *ipaddr,
-				  struct nfsd4_ssc_umount_item **nsui)
+				  struct nfsd4_ssc_umount_item **nsui,
+				  struct svc_rqst *rqstp)
 {
 	struct nfsd4_ssc_umount_item *ni = NULL;
 	struct nfsd4_ssc_umount_item *work = NULL;
@@ -1329,7 +1330,7 @@ static __be32 nfsd4_ssc_setup_dul(struct nfsd_net *nn, char *ipaddr,
 			spin_unlock(&nn->nfsd_ssc_lock);
 
 			/* allow 20secs for mount/unmount for now - revisit */
-			if (kthread_should_stop() ||
+			if (svc_thread_should_stop(rqstp) ||
 					(schedule_timeout(20*HZ) == 0)) {
 				finish_wait(&nn->nfsd_ssc_waitq, &wait);
 				kfree(work);
@@ -1445,7 +1446,7 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
 		goto out_free_rawdata;
 	snprintf(dev_name, len + 5, "%s%s%s:/", startsep, ipaddr, endsep);
 
-	status = nfsd4_ssc_setup_dul(nn, ipaddr, nsui);
+	status = nfsd4_ssc_setup_dul(nn, ipaddr, nsui, rqstp);
 	if (status)
 		goto out_free_devname;
 	if ((*nsui)->nsui_vfsmount)
@@ -1620,6 +1621,7 @@ static ssize_t _nfsd_copy_file_range(struct nfsd4_copy *copy,
 	if (bytes_total == 0)
 		bytes_total = ULLONG_MAX;
 	do {
+		/* Only async copies can be stopped here */
 		if (kthread_should_stop())
 			break;
 		bytes_copied = nfsd_copy_file_range(src, src_pos, dst, dst_pos,
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index b536b254c59e..9b282c89ea87 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -971,7 +971,7 @@ nfsd(void *vrqstp)
 	/*
 	 * The main request loop
 	 */
-	while (!kthread_should_stop()) {
+	while (!svc_thread_should_stop(rqstp)) {
 		/* Update sv_maxconn if it has changed */
 		rqstp->rq_server->sv_maxconn = nn->max_connections;
 
diff --git a/include/linux/lockd/lockd.h b/include/linux/lockd/lockd.h
index 0f016d69c996..9f565416d186 100644
--- a/include/linux/lockd/lockd.h
+++ b/include/linux/lockd/lockd.h
@@ -282,7 +282,7 @@ __be32		  nlmsvc_testlock(struct svc_rqst *, struct nlm_file *,
 			struct nlm_host *, struct nlm_lock *,
 			struct nlm_lock *, struct nlm_cookie *);
 __be32		  nlmsvc_cancel_blocked(struct net *net, struct nlm_file *, struct nlm_lock *);
-void		  nlmsvc_retry_blocked(void);
+void		  nlmsvc_retry_blocked(struct svc_rqst *rqstp);
 void		  nlmsvc_traverse_blocks(struct nlm_host *, struct nlm_file *,
 					nlm_host_match_fn_t match);
 void		  nlmsvc_grant_reply(struct nlm_cookie *, __be32);
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 15d468d852b5..ea3ce1315416 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -51,6 +51,8 @@ struct svc_pool {
 enum {
 	SP_TASK_PENDING,	/* still work to do even if no xprt is queued */
 	SP_CONGESTED,		/* all threads are busy, none idle */
+	SP_NEED_VICTIM,		/* One thread needs to agree to exit */
+	SP_VICTIM_REMAINS,	/* One thread needs to actually exit */
 };
 
 /*
@@ -275,7 +277,7 @@ enum {
 	RQ_DROPME,	/* drop current reply */
 	RQ_SPLICE_OK,	/* turned off in gss privacy to prevent encrypting page
 			 * cache pages */
-	RQ_VICTIM,	/* about to be shut down */
+	RQ_VICTIM,	/* Have agreed to shut down */
 	RQ_BUSY,	/* request is busy */
 	RQ_DATA,	/* request has data */
 };
@@ -315,6 +317,24 @@ static inline struct sockaddr *svc_daddr(const struct svc_rqst *rqst)
 	return (struct sockaddr *) &rqst->rq_daddr;
 }
 
+/**
+ * svc_thread_should_stop - check if this thread should stop
+ * @rqstp: the thread that might need to stop
+ *
+ * To stop an svc thread, the pool flags SP_NEED_VICTIM and SP_VICTIM_REMAINS
+ * are set.  The firs thread which sees SP_NEED_VICTIM clear it becoming
+ * the victim using this function.  It should then promptly call
+ * svc_exit_thread() which completes the process, clearing SP_VICTIM_REMAINS
+ * so the task waiting for a thread to exit can wake and continue.
+ */
+static inline bool svc_thread_should_stop(struct svc_rqst *rqstp)
+{
+	if (test_and_clear_bit(SP_NEED_VICTIM, &rqstp->rq_pool->sp_flags))
+		set_bit(RQ_VICTIM, &rqstp->rq_flags);
+
+	return test_bit(RQ_VICTIM, &rqstp->rq_flags);
+}
+
 struct svc_deferred_req {
 	u32			prot;	/* protocol (UDP or TCP) */
 	struct svc_xprt		*xprt;
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 60c8e03268d4..c79375e37dc2 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -2041,8 +2041,9 @@ TRACE_EVENT(svc_xprt_enqueue,
 #define show_svc_pool_flags(x)						\
 	__print_flags(x, "|",						\
 		{ BIT(SP_TASK_PENDING),		"TASK_PENDING" },	\
-		{ BIT(SP_CONGESTED),		"CONGESTED" })
-
+		{ BIT(SP_CONGESTED),		"CONGESTED" },		\
+		{ BIT(SP_NEED_VICTIM),		"NEED_VICTIM" },	\
+		{ BIT(SP_VICTIM_REMAINS),	"VICTIM_REMAINS" })
 DECLARE_EVENT_CLASS(svc_pool_scheduler_class,
 	TP_PROTO(
 		const struct svc_rqst *rqstp
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 56b4a88776d5..b18175ef74ec 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -731,19 +731,22 @@ svc_pool_next(struct svc_serv *serv, struct svc_pool *pool, unsigned int *state)
 	return pool ? pool : &serv->sv_pools[(*state)++ % serv->sv_nrpools];
 }
 
-static struct task_struct *
+static struct svc_pool *
 svc_pool_victim(struct svc_serv *serv, struct svc_pool *pool, unsigned int *state)
 {
 	unsigned int i;
-	struct task_struct *task = NULL;
 
 	if (pool != NULL) {
 		spin_lock_bh(&pool->sp_lock);
+		if (pool->sp_nrthreads)
+			goto found_pool;
+		spin_unlock_bh(&pool->sp_lock);
+		return NULL;
 	} else {
 		for (i = 0; i < serv->sv_nrpools; i++) {
 			pool = &serv->sv_pools[--(*state) % serv->sv_nrpools];
 			spin_lock_bh(&pool->sp_lock);
-			if (!list_empty(&pool->sp_all_threads))
+			if (pool->sp_nrthreads)
 				goto found_pool;
 			spin_unlock_bh(&pool->sp_lock);
 		}
@@ -751,16 +754,10 @@ svc_pool_victim(struct svc_serv *serv, struct svc_pool *pool, unsigned int *stat
 	}
 
 found_pool:
-	if (!list_empty(&pool->sp_all_threads)) {
-		struct svc_rqst *rqstp;
-
-		rqstp = list_entry(pool->sp_all_threads.next, struct svc_rqst, rq_all);
-		set_bit(RQ_VICTIM, &rqstp->rq_flags);
-		list_del_rcu(&rqstp->rq_all);
-		task = rqstp->rq_task;
-	}
+	set_bit(SP_VICTIM_REMAINS, &pool->sp_flags);
+	set_bit(SP_NEED_VICTIM, &pool->sp_flags);
 	spin_unlock_bh(&pool->sp_lock);
-	return task;
+	return pool;
 }
 
 static int
@@ -801,18 +798,16 @@ svc_start_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
 static int
 svc_stop_kthreads(struct svc_serv *serv, struct svc_pool *pool, int nrservs)
 {
-	struct svc_rqst	*rqstp;
-	struct task_struct *task;
 	unsigned int state = serv->sv_nrthreads-1;
+	struct svc_pool *vpool;
 
 	do {
-		task = svc_pool_victim(serv, pool, &state);
-		if (task == NULL)
+		vpool = svc_pool_victim(serv, pool, &state);
+		if (!vpool)
 			break;
-		rqstp = kthread_data(task);
-		/* Did we lose a race to svo_function threadfn? */
-		if (kthread_stop(task) == -EINTR)
-			svc_exit_thread(rqstp);
+		svc_pool_wake_idle_thread(serv, vpool);
+		wait_on_bit(&vpool->sp_flags, SP_VICTIM_REMAINS,
+			    TASK_IDLE);
 		nrservs++;
 	} while (nrservs < 0);
 	return 0;
@@ -932,8 +927,6 @@ svc_exit_thread(struct svc_rqst *rqstp)
 
 	spin_lock_bh(&pool->sp_lock);
 	pool->sp_nrthreads--;
-	if (!test_and_set_bit(RQ_VICTIM, &rqstp->rq_flags))
-		list_del_rcu(&rqstp->rq_all);
 	spin_unlock_bh(&pool->sp_lock);
 
 	spin_lock_bh(&serv->sv_lock);
@@ -941,6 +934,8 @@ svc_exit_thread(struct svc_rqst *rqstp)
 	spin_unlock_bh(&serv->sv_lock);
 	svc_sock_update_bufs(serv);
 
+	if (svc_thread_should_stop(rqstp))
+		clear_and_wake_up_bit(SP_VICTIM_REMAINS, &pool->sp_flags);
 	svc_rqst_free(rqstp);
 
 	svc_put(serv);
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 4fdf1aaa514b..948605e7043b 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -595,8 +595,6 @@ void svc_wake_up(struct svc_serv *serv)
 		smp_wmb();
 		return;
 	}
-
-	trace_svc_wake_up(rqstp);
 }
 EXPORT_SYMBOL_GPL(svc_wake_up);
 
@@ -688,7 +686,7 @@ static bool svc_alloc_arg(struct svc_rqst *rqstp)
 			continue;
 
 		set_current_state(TASK_IDLE);
-		if (kthread_should_stop()) {
+		if (svc_thread_should_stop(rqstp)) {
 			set_current_state(TASK_RUNNING);
 			return false;
 		}
@@ -726,7 +724,7 @@ rqst_should_sleep(struct svc_rqst *rqstp)
 		return false;
 
 	/* are we shutting down? */
-	if (kthread_should_stop())
+	if (svc_thread_should_stop(rqstp))
 		return false;
 
 	/* are we freezing? */
@@ -787,7 +785,7 @@ static void svc_wait_for_work(struct svc_rqst *rqstp)
 	}
 #endif
 
-	if (!kthread_should_stop())
+	if (!svc_thread_should_stop(rqstp))
 		percpu_counter_inc(&pool->sp_threads_no_work);
 	return;
 out_found: