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From:   NeilBrown <neilb@suse.de>
To:     Chuck Lever <chuck.lever@oracle.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     linux-nfs@vger.kernel.org
Subject: [PATCH 04/12] nfsd: Simplify code around svc_exit_thread() call in nfsd()
Date:   Mon, 31 Jul 2023 16:48:31 +1000
Message-Id: <20230731064839.7729-5-neilb@suse.de>
In-Reply-To: <20230731064839.7729-1-neilb@suse.de>
References: <20230731064839.7729-1-neilb@suse.de>
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Previously a thread could exit asynchronously (due to a signal) so some
care was needed to hold nfsd_mutex over the last svc_put() call.  Now a
thread can only exit when svc_set_num_thread() is called, and this is
always called under nfsd_mutex.  So no care is needed.

Not only is it the mutex held when a thread exits now, but the svc
refcount is elevated, so the svc_put() in svc_exit_thread() will never
be a final put, so the mutex isn't even needed at this point in the
code.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/nfsd/nfssvc.c           | 23 -----------------------
 include/linux/sunrpc/svc.h | 13 -------------
 2 files changed, 36 deletions(-)

diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 82e272707d2f..33a80725e14e 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -982,31 +982,8 @@ nfsd(void *vrqstp)
 	atomic_dec(&nfsdstats.th_cnt);
 
 out:
-	/* Take an extra ref so that the svc_put in svc_exit_thread()
-	 * doesn't call svc_destroy()
-	 */
-	svc_get(nn->nfsd_serv);
-
 	/* Release the thread */
 	svc_exit_thread(rqstp);
-
-	/* We need to drop a ref, but may not drop the last reference
-	 * without holding nfsd_mutex, and we cannot wait for nfsd_mutex as that
-	 * could deadlock with nfsd_shutdown_threads() waiting for us.
-	 * So three options are:
-	 * - drop a non-final reference,
-	 * - get the mutex without waiting
-	 * - sleep briefly andd try the above again
-	 */
-	while (!svc_put_not_last(nn->nfsd_serv)) {
-		if (mutex_trylock(&nfsd_mutex)) {
-			nfsd_put(net);
-			mutex_unlock(&nfsd_mutex);
-			break;
-		}
-		msleep(20);
-	}
-
 	return 0;
 }
 
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 110f4560be38..db3de4ea33f9 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -125,19 +125,6 @@ static inline void svc_put(struct svc_serv *serv)
 	kref_put(&serv->sv_refcnt, svc_destroy);
 }
 
-/**
- * svc_put_not_last - decrement non-final reference count on SUNRPC serv
- * @serv:  the svc_serv to have count decremented
- *
- * Returns: %true is refcount was decremented.
- *
- * If the refcount is 1, it is not decremented and instead failure is reported.
- */
-static inline bool svc_put_not_last(struct svc_serv *serv)
-{
-	return refcount_dec_not_one(&serv->sv_refcnt.refcount);
-}
-
 /*
  * Maximum payload size supported by a kernel RPC server.
  * This is use to determine the max number of pages nfsd is
-- 
2.40.1