linux-kernel - [PATCH 4/8] Drivers: hv: vmbus: Remove unnecessary channel->lock critical sections (sc

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Date:   Wed, 17 Jun 2020 18:46:38 +0200
From:   "Andrea Parri (Microsoft)" <parri.andrea@...il.com>
To:     "K . Y . Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>
Cc:     linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Andrea Parri (Microsoft)" <parri.andrea@...il.com>
Subject: [PATCH 4/8] Drivers: hv: vmbus: Remove unnecessary channel->lock critical sections (sc_list readers)

Additions/deletions to/from sc_list (as well as modifications of
target_cpu(s)) are protected by channel_mutex, which hv_synic_cleanup()
and vmbus_bus_suspend() own for the duration of the channel->lock
critical section in question.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
---
 drivers/hv/hv.c        | 3 ---
 drivers/hv/vmbus_drv.c | 3 ---
 2 files changed, 6 deletions(-)

diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 188b42b07f07b..0c637111e7c70 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -245,7 +245,6 @@ int hv_synic_cleanup(unsigned int cpu)
 {
 	struct vmbus_channel *channel, *sc;
 	bool channel_found = false;
-	unsigned long flags;
 
 	/*
 	 * Hyper-V does not provide a way to change the connect CPU once
@@ -267,14 +266,12 @@ int hv_synic_cleanup(unsigned int cpu)
 			channel_found = true;
 			break;
 		}
-		spin_lock_irqsave(&channel->lock, flags);
 		list_for_each_entry(sc, &channel->sc_list, sc_list) {
 			if (sc->target_cpu == cpu) {
 				channel_found = true;
 				break;
 			}
 		}
-		spin_unlock_irqrestore(&channel->lock, flags);
 		if (channel_found)
 			break;
 	}
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 452c14c656e2a..b5ae45eb8aef7 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2330,7 +2330,6 @@ static int vmbus_acpi_add(struct acpi_device *device)
 static int vmbus_bus_suspend(struct device *dev)
 {
 	struct vmbus_channel *channel, *sc;
-	unsigned long flags;
 
 	while (atomic_read(&vmbus_connection.offer_in_progress) != 0) {
 		/*
@@ -2388,12 +2387,10 @@ static int vmbus_bus_suspend(struct device *dev)
 			continue;
 		}
 
-		spin_lock_irqsave(&channel->lock, flags);
 		list_for_each_entry(sc, &channel->sc_list, sc_list) {
 			pr_err("Sub-channel not deleted!\n");
 			WARN_ON_ONCE(1);
 		}
-		spin_unlock_irqrestore(&channel->lock, flags);
 
 		atomic_inc(&vmbus_connection.nr_chan_fixup_on_resume);
 	}
-- 
2.25.1