[PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[Dexuan Cui]

In the SMP guest case, when the per-channel callback hvsock_events() is
running on virtual CPU A, if the guest tries to close the connection on
virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
then we can have trouble: on B, vmbus_close_internal() will send IPI
reset_channel_cb() to A, trying to set channel->onchannel_callbackto NULL;
on A, if the IPI handler happens between
"if (channel->onchannel_callback != NULL)" and invoking
channel->onchannel_callback, we'll invoke a function pointer of NULL.

This is why the patch is necessary.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 drivers/hv/connection.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 4fc2e88..4766fd8 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -319,6 +319,9 @@ static void process_chn_event(u32 relid)
 	void *arg;
 	bool read_state;
 	u32 bytes_to_read;
+	bool is_hvsock = false;
+
+	local_irq_disable();
 
 	/*
 	 * Find the channel based on this relid and invokes the
@@ -327,7 +330,11 @@ static void process_chn_event(u32 relid)
 	channel = pcpu_relid2channel(relid);
 
 	if (!channel)
-		return;
+		goto out;
+
+	is_hvsock = is_hvsock_channel(channel);
+	if (!is_hvsock)
+		local_irq_enable();
 
 	/*
 	 * A channel once created is persistent even when there
@@ -363,6 +370,12 @@ static void process_chn_event(u32 relid)
 				bytes_to_read = 0;
 		} while (read_state && (bytes_to_read != 0));
 	}
+
+	/* local_irq_enable() is alredy invoked above */
+	if (!is_hvsock)
+		return;
+out:
+	local_irq_enable();
 }
 
 /*
-- 
2.1.0

Re: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[David Miller]

From: Dexuan Cui <decui@microsoft.com>
Date: Tue, 28 Jul 2015 05:35:30 -0700

> In the SMP guest case, when the per-channel callback hvsock_events() is
> running on virtual CPU A, if the guest tries to close the connection on
> virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
> then we can have trouble: on B, vmbus_close_internal() will send IPI
> reset_channel_cb() to A, trying to set channel->onchannel_callbackto NULL;
> on A, if the IPI handler happens between
> "if (channel->onchannel_callback != NULL)" and invoking
> channel->onchannel_callback, we'll invoke a function pointer of NULL.
> 
> This is why the patch is necessary.
> 
> Signed-off-by: Dexuan Cui <decui@microsoft.com>

Sorry, I do not accept that you must use conditional locking and/or
IRQ disabling.

Boil it down to what is necessary for the least common denominator,
and use that unconditionally.

RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[Dexuan Cui]

> From: David Miller
> Sent: Thursday, July 30, 2015 6:28
> > From: Dexuan Cui <decui@microsoft.com>
> > Date: Tue, 28 Jul 2015 05:35:30 -0700
> >
> > In the SMP guest case, when the per-channel callback hvsock_events() is
> > running on virtual CPU A, if the guest tries to close the connection on
> > virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
> > then we can have trouble: on B, vmbus_close_internal() will send IPI
> > reset_channel_cb() to A, trying to set channel->onchannel_callbackto NULL;
> > on A, if the IPI handler happens between
> > "if (channel->onchannel_callback != NULL)" and invoking
> > channel->onchannel_callback, we'll invoke a function pointer of NULL.
> >
> > This is why the patch is necessary.
> >
> Sorry, I do not accept that you must use conditional locking and/or
> IRQ disabling.
>
> Boil it down to what is necessary for the least common denominator,
> and use that unconditionally.

Hi David,
Thanks for the comment!

I agree with you it's not clean to use conditional IRQ disabling.

Here I didn't use unconditionally IRQ disabling because the Hyper-V netvsc
and storvsc driver's vmbus event callbacks (i.e. netvsc_channel_cb() and
storvsc_on_channel_callback()) may take relatively long time (e.g., netvsc can
operate at a speed of 10Gb) and I think it's bad to disable IRQ for long time
when the callbacks are running in a tasklet context, e.g., the Hyper-V timer
can be affected: see vmbus_isr() -> hv_process_timer_expiration().

To resolve the race condition between vmbus_close_internal() and
process_chn_event() in SMP case, now I propose a new method:

we can serialize the 2 paths by adding
tasklet_disable(hv_context.event_dpc[channel->target_cpu]) and
tasklet_enable(...) in vmbus_close_internal().

In this way, we need the least change and we can drop this patch.

Please let me know your opinion.

Thanks,
-- Dexuan

RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[Dexuan Cui]

> -----Original Message-----
> From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On Behalf
> Of Dexuan Cui
> Sent: Thursday, July 30, 2015 18:18
> To: David Miller <davem@davemloft.net>; KY Srinivasan <kys@microsoft.com>
> Cc: olaf@aepfle.de; gregkh@linuxfoundation.org; jasowang@redhat.com;
> driverdev-devel@linuxdriverproject.org; linux-kernel@vger.kernel.org;
> stephen@networkplumber.org; stefanha@redhat.com; netdev@vger.kernel.org;
> apw@canonical.com; pebolle@tiscali.nl; dan.carpenter@oracle.com
> Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when
> hvsock's callback is running
> 
> > From: David Miller
> > Sent: Thursday, July 30, 2015 6:28
> > > From: Dexuan Cui <decui@microsoft.com>
> > > Date: Tue, 28 Jul 2015 05:35:30 -0700
> > >
> > > In the SMP guest case, when the per-channel callback hvsock_events() is
> > > running on virtual CPU A, if the guest tries to close the connection on
> > > virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
> > > then we can have trouble: on B, vmbus_close_internal() will send IPI
> > > reset_channel_cb() to A, trying to set channel->onchannel_callbackto NULL;
> > > on A, if the IPI handler happens between
> > > "if (channel->onchannel_callback != NULL)" and invoking
> > > channel->onchannel_callback, we'll invoke a function pointer of NULL.
> > >
> > > This is why the patch is necessary.
> > >
> > Sorry, I do not accept that you must use conditional locking and/or
> > IRQ disabling.
> >
> > Boil it down to what is necessary for the least common denominator,
> > and use that unconditionally.
> 
> Hi David,
> Thanks for the comment!
> 
> I agree with you it's not clean to use conditional IRQ disabling.
> 
> Here I didn't use unconditionally IRQ disabling because the Hyper-V netvsc
> and storvsc driver's vmbus event callbacks (i.e. netvsc_channel_cb() and
> storvsc_on_channel_callback()) may take relatively long time (e.g., netvsc can
> operate at a speed of 10Gb) and I think it's bad to disable IRQ for long time
> when the callbacks are running in a tasklet context, e.g., the Hyper-V timer
> can be affected: see vmbus_isr() -> hv_process_timer_expiration().
> 
> To resolve the race condition between vmbus_close_internal() and
> process_chn_event() in SMP case, now I propose a new method:
> 
> we can serialize the 2 paths by adding
> tasklet_disable(hv_context.event_dpc[channel->target_cpu]) and
> tasklet_enable(...) in vmbus_close_internal().
> 
> In this way, we need the least change and we can drop this patch.
> 
> Please let me know your opinion.
> 
> -- Dexuan

Hi David, KY and all,

May I know your opinion about my idea of adding tasklet_disable/enbable()
in vmbus_close_internal() and dropping this patch?

Thanks,
-- Dexuan

RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[KY Srinivasan]

> -----Original Message-----
> From: Dexuan Cui
> Sent: Wednesday, August 5, 2015 9:44 PM
> To: David Miller <davem@davemloft.net>; KY Srinivasan
> <kys@microsoft.com>
> Cc: olaf@aepfle.de; gregkh@linuxfoundation.org; jasowang@redhat.com;
> driverdev-devel@linuxdriverproject.org; linux-kernel@vger.kernel.org;
> stephen@networkplumber.org; stefanha@redhat.com;
> netdev@vger.kernel.org; apw@canonical.com; pebolle@tiscali.nl;
> dan.carpenter@oracle.com
> Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when
> hvsock's callback is running
> 
> > -----Original Message-----
> > From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On
> Behalf
> > Of Dexuan Cui
> > Sent: Thursday, July 30, 2015 18:18
> > To: David Miller <davem@davemloft.net>; KY Srinivasan
> <kys@microsoft.com>
> > Cc: olaf@aepfle.de; gregkh@linuxfoundation.org; jasowang@redhat.com;
> > driverdev-devel@linuxdriverproject.org; linux-kernel@vger.kernel.org;
> > stephen@networkplumber.org; stefanha@redhat.com;
> netdev@vger.kernel.org;
> > apw@canonical.com; pebolle@tiscali.nl; dan.carpenter@oracle.com
> > Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt
> when
> > hvsock's callback is running
> >
> > > From: David Miller
> > > Sent: Thursday, July 30, 2015 6:28
> > > > From: Dexuan Cui <decui@microsoft.com>
> > > > Date: Tue, 28 Jul 2015 05:35:30 -0700
> > > >
> > > > In the SMP guest case, when the per-channel callback hvsock_events()
> is
> > > > running on virtual CPU A, if the guest tries to close the connection on
> > > > virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
> > > > then we can have trouble: on B, vmbus_close_internal() will send IPI
> > > > reset_channel_cb() to A, trying to set channel->onchannel_callbackto
> NULL;
> > > > on A, if the IPI handler happens between
> > > > "if (channel->onchannel_callback != NULL)" and invoking
> > > > channel->onchannel_callback, we'll invoke a function pointer of NULL.
> > > >
> > > > This is why the patch is necessary.
> > > >
> > > Sorry, I do not accept that you must use conditional locking and/or
> > > IRQ disabling.
> > >
> > > Boil it down to what is necessary for the least common denominator,
> > > and use that unconditionally.
> >
> > Hi David,
> > Thanks for the comment!
> >
> > I agree with you it's not clean to use conditional IRQ disabling.
> >
> > Here I didn't use unconditionally IRQ disabling because the Hyper-V netvsc
> > and storvsc driver's vmbus event callbacks (i.e. netvsc_channel_cb() and
> > storvsc_on_channel_callback()) may take relatively long time (e.g., netvsc
> can
> > operate at a speed of 10Gb) and I think it's bad to disable IRQ for long time
> > when the callbacks are running in a tasklet context, e.g., the Hyper-V timer
> > can be affected: see vmbus_isr() -> hv_process_timer_expiration().
> >
> > To resolve the race condition between vmbus_close_internal() and
> > process_chn_event() in SMP case, now I propose a new method:
> >
> > we can serialize the 2 paths by adding
> > tasklet_disable(hv_context.event_dpc[channel->target_cpu]) and
> > tasklet_enable(...) in vmbus_close_internal().
> >
> > In this way, we need the least change and we can drop this patch.
> >
> > Please let me know your opinion.
> >
> > -- Dexuan
> 
> Hi David, KY and all,
> 
> May I know your opinion about my idea of adding tasklet_disable/enbable()
> in vmbus_close_internal() and dropping this patch?

Sorry for the delayed response; I think this is a reasonable solution. Send me the patch.

Regards,

K. Y
> 
> Thanks,
> -- Dexuan

RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when hvsock's callback is running

[Dexuan Cui]

> From: KY Srinivasan
> Sent: Friday, August 7, 2015 1:50
> To: Dexuan Cui <decui@microsoft.com>; David Miller <davem@davemloft.net>
> Cc: olaf@aepfle.de; gregkh@linuxfoundation.org; jasowang@redhat.com;
> driverdev-devel@linuxdriverproject.org; linux-kernel@vger.kernel.org;
> stephen@networkplumber.org; stefanha@redhat.com; netdev@vger.kernel.org;
> apw@canonical.com; pebolle@tiscali.nl; dan.carpenter@oracle.com
> Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when
> hvsock's callback is running
> > From: Dexuan Cui
> > Sent: Wednesday, August 5, 2015 9:44 PM
> > To: David Miller <davem@davemloft.net>; KY Srinivasan
> > <kys@microsoft.com>
> > Cc: olaf@aepfle.de; gregkh@linuxfoundation.org; jasowang@redhat.com;
> > driverdev-devel@linuxdriverproject.org; linux-kernel@vger.kernel.org;
> > stephen@networkplumber.org; stefanha@redhat.com;
> > netdev@vger.kernel.org; apw@canonical.com; pebolle@tiscali.nl;
> > dan.carpenter@oracle.com
> > Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt when
> > hvsock's callback is running
> >
> > > From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On
> > Behalf
> > > Of Dexuan Cui
> > > Sent: Thursday, July 30, 2015 18:18
> > > To: David Miller <davem@davemloft.net>; KY Srinivasan
> > <kys@microsoft.com>
> > > Cc: olaf@aepfle.de; gregkh@linuxfoundation.org; jasowang@redhat.com;
> > > driverdev-devel@linuxdriverproject.org; linux-kernel@vger.kernel.org;
> > > stephen@networkplumber.org; stefanha@redhat.com;
> > netdev@vger.kernel.org;
> > > apw@canonical.com; pebolle@tiscali.nl; dan.carpenter@oracle.com
> > > Subject: RE: [PATCH V4 7/7] Drivers: hv: vmbus: disable local interrupt
> > when
> > > hvsock's callback is running
> > >
> > > > From: David Miller
> > > > Sent: Thursday, July 30, 2015 6:28
> > > > > From: Dexuan Cui <decui@microsoft.com>
> > > > > Date: Tue, 28 Jul 2015 05:35:30 -0700
> > > > >
> > > > > In the SMP guest case, when the per-channel callback hvsock_events()
> > is
> > > > > running on virtual CPU A, if the guest tries to close the connection on
> > > > > virtual CPU B: we invoke vmbus_close() -> vmbus_close_internal(),
> > > > > then we can have trouble: on B, vmbus_close_internal() will send IPI
> > > > > reset_channel_cb() to A, trying to set channel->onchannel_callbackto
> > NULL;
> > > > > on A, if the IPI handler happens between
> > > > > "if (channel->onchannel_callback != NULL)" and invoking
> > > > > channel->onchannel_callback, we'll invoke a function pointer of NULL.
> > > > >
> > > > > This is why the patch is necessary.
> > > > >
> > > > Sorry, I do not accept that you must use conditional locking and/or
> > > > IRQ disabling.
> > > >
> > > > Boil it down to what is necessary for the least common denominator,
> > > > and use that unconditionally.
> > >
> > > Hi David,
> > > Thanks for the comment!
> > >
> > > I agree with you it's not clean to use conditional IRQ disabling.
> > >
> > > Here I didn't use unconditionally IRQ disabling because the Hyper-V netvsc
> > > and storvsc driver's vmbus event callbacks (i.e. netvsc_channel_cb() and
> > > storvsc_on_channel_callback()) may take relatively long time (e.g., netvsc
> > can
> > > operate at a speed of 10Gb) and I think it's bad to disable IRQ for long time
> > > when the callbacks are running in a tasklet context, e.g., the Hyper-V timer
> > > can be affected: see vmbus_isr() -> hv_process_timer_expiration().
> > >
> > > To resolve the race condition between vmbus_close_internal() and
> > > process_chn_event() in SMP case, now I propose a new method:
> > >
> > > we can serialize the 2 paths by adding
> > > tasklet_disable(hv_context.event_dpc[channel->target_cpu]) and
> > > tasklet_enable(...) in vmbus_close_internal().
> > >
> > > In this way, we need the least change and we can drop this patch.
> > >
> > > Please let me know your opinion.
> > >
> > > -- Dexuan
> >
> > Hi David, KY and all,
> >
> > May I know your opinion about my idea of adding tasklet_disable/enbable()
> > in vmbus_close_internal() and dropping this patch?
> 
> Sorry for the delayed response; I think this is a reasonable solution. Send me the
> patch.
> 
> Regards,
> 
> K. Y

OK. Will do.

 Thanks,
 -- Dexuan