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Commit dad72a1d authored by Dexuan Cui's avatar Dexuan Cui Committed by Greg Kroah-Hartman
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vmbus: remove hv_event_tasklet_disable/enable 



With the recent introduction of per-channel tasklet, we need to update
the way we handle the 3 concurrency issues:

1. hv_process_channel_removal -> percpu_channel_deq vs.
   vmbus_chan_sched -> list_for_each_entry(..., percpu_list);

2. vmbus_process_offer -> percpu_channel_enq/deq vs. vmbus_chan_sched.

3. vmbus_close_internal vs. the per-channel tasklet vmbus_on_event;

The first 2 issues can be handled by Stephen's recent patch
"vmbus: use rcu for per-cpu channel list", and the third issue
can be handled by calling tasklet_disable in vmbus_close_internal here.

We don't need the original hv_event_tasklet_disable/enable since we
now use per-channel tasklet instead of the previous per-CPU tasklet,
and actually we must remove them due to the side effect now:
vmbus_process_offer -> hv_event_tasklet_enable -> tasklet_schedule will
start the per-channel callback prematurely, cauing NULL dereferencing
(the channel may haven't been properly configured to run the callback yet).

Fixes: 631e63a9 ("vmbus: change to per channel tasklet")

Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Tested-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 8200f208

drivers/hv/channel.c

+4 −8
Original line number Diff line number Diff line
@@ -530,15 +530,13 @@ static int vmbus_close_internal(struct vmbus_channel *channel) 
	int ret;



	/*

	 * vmbus_on_event(), running in the tasklet, can race

	 * vmbus_on_event(), running in the per-channel tasklet, can race

	 * with vmbus_close_internal() in the case of SMP guest, e.g., when

	 * the former is accessing channel->inbound.ring_buffer, the latter

	 * could be freeing the ring_buffer pages.

	 *

	 * To resolve the race, we can serialize them by disabling the

	 * tasklet when the latter is running here.

	 * could be freeing the ring_buffer pages, so here we must stop it

	 * first.

	 */

	hv_event_tasklet_disable(channel);

	tasklet_disable(&channel->callback_event);



	/*

	 * In case a device driver's probe() fails (e.g.,
@@ -605,8 +603,6 @@ static int vmbus_close_internal(struct vmbus_channel *channel) 
		get_order(channel->ringbuffer_pagecount * PAGE_SIZE));



out:

	hv_event_tasklet_enable(channel);



	return ret;

}

drivers/hv/channel_mgmt.c

+0 −19
Original line number Diff line number Diff line
@@ -382,19 +382,6 @@ static void vmbus_release_relid(u32 relid) 
		       true);

}



void hv_event_tasklet_disable(struct vmbus_channel *channel)

{

	tasklet_disable(&channel->callback_event);

}



void hv_event_tasklet_enable(struct vmbus_channel *channel)

{

	tasklet_enable(&channel->callback_event);



	/* In case there is any pending event */

	tasklet_schedule(&channel->callback_event);

}



void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid)

{

	unsigned long flags;
@@ -403,7 +390,6 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid) 
	BUG_ON(!channel->rescind);

	BUG_ON(!mutex_is_locked(&vmbus_connection.channel_mutex));



	hv_event_tasklet_disable(channel);

	if (channel->target_cpu != get_cpu()) {

		put_cpu();

		smp_call_function_single(channel->target_cpu,
@@ -412,7 +398,6 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid) 
		percpu_channel_deq(channel);

		put_cpu();

	}

	hv_event_tasklet_enable(channel);



	if (channel->primary_channel == NULL) {

		list_del(&channel->listentry);
@@ -506,7 +491,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) 


	init_vp_index(newchannel, dev_type);



	hv_event_tasklet_disable(newchannel);

	if (newchannel->target_cpu != get_cpu()) {

		put_cpu();

		smp_call_function_single(newchannel->target_cpu,
@@ -516,7 +500,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) 
		percpu_channel_enq(newchannel);

		put_cpu();

	}

	hv_event_tasklet_enable(newchannel);



	/*

	 * This state is used to indicate a successful open
@@ -566,7 +549,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) 
	list_del(&newchannel->listentry);

	mutex_unlock(&vmbus_connection.channel_mutex);



	hv_event_tasklet_disable(newchannel);

	if (newchannel->target_cpu != get_cpu()) {

		put_cpu();

		smp_call_function_single(newchannel->target_cpu,
@@ -575,7 +557,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) 
		percpu_channel_deq(newchannel);

		put_cpu();

	}

	hv_event_tasklet_enable(newchannel);



	vmbus_release_relid(newchannel->offermsg.child_relid);

include/linux/hyperv.h

+0 −3
Original line number Diff line number Diff line
@@ -1437,9 +1437,6 @@ extern bool vmbus_prep_negotiate_resp(struct icmsg_hdr *icmsghdrp, u8 *buf, 
				const int *srv_version, int srv_vercnt,

				int *nego_fw_version, int *nego_srv_version);



void hv_event_tasklet_disable(struct vmbus_channel *channel);

void hv_event_tasklet_enable(struct vmbus_channel *channel);



void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid);



void vmbus_setevent(struct vmbus_channel *channel);