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Commit 41571916 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Greg Kroah-Hartman
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Drivers: hv: vmbus: avoid scheduling in interrupt context in vmbus_initiate_unload() 



We have to call vmbus_initiate_unload() on crash to make kdump work but
the crash can also be happening in interrupt (e.g. Sysrq + c results in
such) where we can't schedule or the following will happen:

[  314.905786] bad: scheduling from the idle thread!

Just skipping the wait (and even adding some random wait here) won't help:
to make host-side magic working we're supposed to receive CHANNELMSG_UNLOAD
(and actually confirm the fact that we received it) but we can't use
interrupt-base path (vmbus_isr()-> vmbus_on_msg_dpc()). Implement a simple
busy wait ignoring all the other messages and use it if we're in an
interrupt context.

Signed-off-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 79fd8e70

drivers/hv/channel_mgmt.c

+43 −1
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ 
#include <linux/list.h>

#include <linux/module.h>

#include <linux/completion.h>

#include <linux/delay.h>

#include <linux/hyperv.h>



#include "hyperv_vmbus.h"
@@ -589,6 +590,40 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type) 
	channel->target_vp = hv_context.vp_index[cur_cpu];

}



static void vmbus_wait_for_unload(void)

{

	int cpu = smp_processor_id();

	void *page_addr = hv_context.synic_message_page[cpu];

	struct hv_message *msg = (struct hv_message *)page_addr +

				  VMBUS_MESSAGE_SINT;

	struct vmbus_channel_message_header *hdr;

	bool unloaded = false;



	while (1) {

		if (msg->header.message_type == HVMSG_NONE) {

			mdelay(10);

			continue;

		}



		hdr = (struct vmbus_channel_message_header *)msg->u.payload;

		if (hdr->msgtype == CHANNELMSG_UNLOAD_RESPONSE)

			unloaded = true;



		msg->header.message_type = HVMSG_NONE;

		/*

		 * header.message_type needs to be written before we do

		 * wrmsrl() below.

		 */

		mb();



		if (msg->header.message_flags.msg_pending)

			wrmsrl(HV_X64_MSR_EOM, 0);



		if (unloaded)

			break;

	}

}



/*

 * vmbus_unload_response - Handler for the unload response.

 */
@@ -614,7 +649,14 @@ void vmbus_initiate_unload(void) 
	hdr.msgtype = CHANNELMSG_UNLOAD;

	vmbus_post_msg(&hdr, sizeof(struct vmbus_channel_message_header));



	/*

	 * vmbus_initiate_unload() is also called on crash and the crash can be

	 * happening in an interrupt context, where scheduling is impossible.

	 */

	if (!in_interrupt())

		wait_for_completion(&vmbus_connection.unload_event);

	else

		vmbus_wait_for_unload();

}



/*