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From:   "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
To:     "K . Y . Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        Michael Kelley <mikelley@microsoft.com>
Cc:     linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
Subject: [PATCH 6/8] Drivers: hv: vmbus: Remove unnecessary channel->lock critical sections (sc_list updaters)
Date:   Wed, 17 Jun 2020 18:46:40 +0200
Message-Id: <20200617164642.37393-7-parri.andrea@gmail.com>
In-Reply-To: <20200617164642.37393-1-parri.andrea@gmail.com>
References: <20200617164642.37393-1-parri.andrea@gmail.com>
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None of the readers/updaters of sc_list rely on channel->lock for
synchronization.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
---
 drivers/hv/channel_mgmt.c | 25 ++++++-------------------
 1 file changed, 6 insertions(+), 19 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 36dd8b6c544a4..92f8bb2077a94 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -400,8 +400,6 @@ static void vmbus_release_relid(u32 relid)
 
 void hv_process_channel_removal(struct vmbus_channel *channel)
 {
-	unsigned long flags;
-
 	lockdep_assert_held(&vmbus_connection.channel_mutex);
 	BUG_ON(!channel->rescind);
 
@@ -422,14 +420,10 @@ void hv_process_channel_removal(struct vmbus_channel *channel)
 	if (channel->offermsg.child_relid != INVALID_RELID)
 		vmbus_channel_unmap_relid(channel);
 
-	if (channel->primary_channel == NULL) {
+	if (channel->primary_channel == NULL)
 		list_del(&channel->listentry);
-	} else {
-		struct vmbus_channel *primary_channel = channel->primary_channel;
-		spin_lock_irqsave(&primary_channel->lock, flags);
+	else
 		list_del(&channel->sc_list);
-		spin_unlock_irqrestore(&primary_channel->lock, flags);
-	}
 
 	/*
 	 * If this is a "perf" channel, updates the hv_numa_map[] masks so that
@@ -470,7 +464,6 @@ static void vmbus_add_channel_work(struct work_struct *work)
 	struct vmbus_channel *newchannel =
 		container_of(work, struct vmbus_channel, add_channel_work);
 	struct vmbus_channel *primary_channel = newchannel->primary_channel;
-	unsigned long flags;
 	int ret;
 
 	/*
@@ -531,13 +524,10 @@ static void vmbus_add_channel_work(struct work_struct *work)
 	 */
 	newchannel->probe_done = true;
 
-	if (primary_channel == NULL) {
+	if (primary_channel == NULL)
 		list_del(&newchannel->listentry);
-	} else {
-		spin_lock_irqsave(&primary_channel->lock, flags);
+	else
 		list_del(&newchannel->sc_list);
-		spin_unlock_irqrestore(&primary_channel->lock, flags);
-	}
 
 	/* vmbus_process_offer() has mapped the channel. */
 	vmbus_channel_unmap_relid(newchannel);
@@ -557,7 +547,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 {
 	struct vmbus_channel *channel;
 	struct workqueue_struct *wq;
-	unsigned long flags;
 	bool fnew = true;
 
 	/*
@@ -609,10 +598,10 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 		}
 	}
 
-	if (fnew)
+	if (fnew) {
 		list_add_tail(&newchannel->listentry,
 			      &vmbus_connection.chn_list);
-	else {
+	} else {
 		/*
 		 * Check to see if this is a valid sub-channel.
 		 */
@@ -630,9 +619,7 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel)
 		 * Process the sub-channel.
 		 */
 		newchannel->primary_channel = channel;
-		spin_lock_irqsave(&channel->lock, flags);
 		list_add_tail(&newchannel->sc_list, &channel->sc_list);
-		spin_unlock_irqrestore(&channel->lock, flags);
 	}
 
 	vmbus_channel_map_relid(newchannel);
-- 
2.25.1