From: "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
Date: Wed, 17 Jun 2020 18:46:38 +0200
Patch-mainline: v5.9-rc1
Subject: Drivers: hv: vmbus: Remove unnecessary channel->lock critical sections (sc_list readers)
Git-commit: 12d0dd8e728e785e6fb81f5232280678bc69d8dc
References: jsc#sle-12891

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@gmail.com>
Link: https://lore.kernel.org/r/20200617164642.37393-5-parri.andrea@gmail.com
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Acked-by: Olaf Hering <ohering@suse.de>
---
 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
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -241,7 +241,6 @@ 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
@@ -263,14 +262,12 @@ 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
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2344,7 +2344,6 @@ acpi_walk_err:
 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) {
 		/*
@@ -2402,12 +2401,10 @@ 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);
 	}