2020-06-17 16:50:24

by Andrea Parri

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) <[email protected]>
---
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

2020-06-18 21:36:19

by Michael Kelley (LINUX)

Subject: RE: [PATCH 4/8] Drivers: hv: vmbus: Remove unnecessary channel->lock critical sections (sc_list readers)

From: Andrea Parri (Microsoft) <[email protected]> Sent: Wednesday, June 17, 2020 9:47 AM
>
> 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) <[email protected]>
> ---
> drivers/hv/hv.c | 3 ---
> drivers/hv/vmbus_drv.c | 3 ---
> 2 files changed, 6 deletions(-)
>

Reviewed-by: Michael Kelley <[email protected]>