2020-04-06 00:18:41

by Andrea Parri

Subject: [PATCH 05/11] hv_utils: Always execute the fcopy and vss callbacks in a tasklet

The fcopy and vss callback functions could be running in a tasklet
at the same time they are called in hv_poll_channel(). Current code
serializes the invocations of these functions, and their accesses to
the channel ring buffer, by sending an IPI to the CPU that is allowed
to access the ring buffer, cf. hv_poll_channel(). This IPI mechanism
becomes infeasible if we allow changing the CPU that a channel will
interrupt. Instead modify the callback wrappers to always execute
the fcopy and vss callbacks in a tasklet, thus mirroring the solution
for the kvp callback functions adopted since commit a3ade8cc474d8
("HV: properly delay KVP packets when negotiation is in progress").
This will ensure that the callback function can't run on two CPUs at
the same time.

Suggested-by: Michael Kelley <[email protected]>
Signed-off-by: Andrea Parri (Microsoft) <[email protected]>
---
drivers/hv/hv_fcopy.c | 2 +-
drivers/hv/hv_snapshot.c | 2 +-
drivers/hv/hyperv_vmbus.h | 7 +------
3 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c
index bb9ba3f7c7949..5040d7e0cd9e9 100644
--- a/drivers/hv/hv_fcopy.c
+++ b/drivers/hv/hv_fcopy.c
@@ -71,7 +71,7 @@ static void fcopy_poll_wrapper(void *channel)
{
/* Transaction is finished, reset the state here to avoid races. */
fcopy_transaction.state = HVUTIL_READY;
- hv_fcopy_onchannelcallback(channel);
+ tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
}

static void fcopy_timeout_func(struct work_struct *dummy)
diff --git a/drivers/hv/hv_snapshot.c b/drivers/hv/hv_snapshot.c
index 1c75b38f0d6da..783779e4cc1a5 100644
--- a/drivers/hv/hv_snapshot.c
+++ b/drivers/hv/hv_snapshot.c
@@ -80,7 +80,7 @@ static void vss_poll_wrapper(void *channel)
{
/* Transaction is finished, reset the state here to avoid races. */
vss_transaction.state = HVUTIL_READY;
- hv_vss_onchannelcallback(channel);
+ tasklet_schedule(&((struct vmbus_channel *)channel)->callback_event);
}

/*
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 41b7267da529a..8df138f98e9e5 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -377,12 +377,7 @@ static inline void hv_poll_channel(struct vmbus_channel *channel,
{
if (!channel)
return;
-
- if (in_interrupt() && (channel->target_cpu == smp_processor_id())) {
- cb(channel);
- return;
- }
- smp_call_function_single(channel->target_cpu, cb, channel, true);
+ cb(channel);
}

enum hvutil_device_state {
--
2.24.0

2020-04-10 19:27:55

by Michael Kelley (LINUX)

Subject: RE: [PATCH 05/11] hv_utils: Always execute the fcopy and vss callbacks in a tasklet

From: Andrea Parri (Microsoft) <[email protected]> Sent: Sunday, April 5, 2020 5:15 PM
>
> The fcopy and vss callback functions could be running in a tasklet
> at the same time they are called in hv_poll_channel(). Current code
> serializes the invocations of these functions, and their accesses to
> the channel ring buffer, by sending an IPI to the CPU that is allowed
> to access the ring buffer, cf. hv_poll_channel(). This IPI mechanism
> becomes infeasible if we allow changing the CPU that a channel will
> interrupt. Instead modify the callback wrappers to always execute
> the fcopy and vss callbacks in a tasklet, thus mirroring the solution
> for the kvp callback functions adopted since commit a3ade8cc474d8
> ("HV: properly delay KVP packets when negotiation is in progress").
> This will ensure that the callback function can't run on two CPUs at
> the same time.
>
> Suggested-by: Michael Kelley <[email protected]>
> Signed-off-by: Andrea Parri (Microsoft) <[email protected]>
> ---
> drivers/hv/hv_fcopy.c | 2 +-
> drivers/hv/hv_snapshot.c | 2 +-
> drivers/hv/hyperv_vmbus.h | 7 +------
> 3 files changed, 3 insertions(+), 8 deletions(-)
>

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