From e3c26a054bfd52d590a07a70db9059f164dc4a24 Mon Sep 17 00:00:00 2001
From: lorneli <lorneli@163.com>
Date: Sat, 29 Dec 2018 21:16:17 +0800
Subject: [PATCH] bdev: reduce critical area in spdk_bdev_open

Since bdev->internal.mutex protects variables in bdev->internal,
there's no need to init the fields of spdk_bdev_desc struct and
free the struct when claim_module exists within the mutex lock.

Reducing critical area could help to reduce lock competition
caused by opening bdev concurrently.

Change-Id: Ie6b2a63e44a97cfed914fa6d8adef2c5ec3ac300
Signed-off-by: lorneli <lorneli@163.com>
Reviewed-on: https://review.gerrithub.io/c/438514
Reviewed-by: wuzhouhui <wuzhouhui@kingsoft.com>
Reviewed-by: GangCao <gang.cao@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
---
 lib/bdev/bdev.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/lib/bdev/bdev.c b/lib/bdev/bdev.c
index 8e4330822..8d5c4de0a 100644
--- a/lib/bdev/bdev.c
+++ b/lib/bdev/bdev.c
@@ -3624,18 +3624,6 @@ spdk_bdev_open(struct spdk_bdev *bdev, bool write, spdk_bdev_remove_cb_t remove_
 	SPDK_DEBUGLOG(SPDK_LOG_BDEV, "Opening descriptor %p for bdev %s on thread %p\n", desc, bdev->name,
 		      spdk_get_thread());
 
-	pthread_mutex_lock(&bdev->internal.mutex);
-
-	if (write && bdev->internal.claim_module) {
-		SPDK_ERRLOG("Could not open %s - %s module already claimed it\n",
-			    bdev->name, bdev->internal.claim_module->name);
-		free(desc);
-		pthread_mutex_unlock(&bdev->internal.mutex);
-		return -EPERM;
-	}
-
-	TAILQ_INSERT_TAIL(&bdev->internal.open_descs, desc, link);
-
 	desc->bdev = bdev;
 	desc->thread = thread;
 	desc->remove_cb = remove_cb;
@@ -3643,6 +3631,19 @@ spdk_bdev_open(struct spdk_bdev *bdev, bool write, spdk_bdev_remove_cb_t remove_
 	desc->write = write;
 	*_desc = desc;
 
+	pthread_mutex_lock(&bdev->internal.mutex);
+
+	if (write && bdev->internal.claim_module) {
+		SPDK_ERRLOG("Could not open %s - %s module already claimed it\n",
+			    bdev->name, bdev->internal.claim_module->name);
+		pthread_mutex_unlock(&bdev->internal.mutex);
+		free(desc);
+		*_desc = NULL;
+		return -EPERM;
+	}
+
+	TAILQ_INSERT_TAIL(&bdev->internal.open_descs, desc, link);
+
 	pthread_mutex_unlock(&bdev->internal.mutex);
 
 	return 0;