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Drivers: hv: vmbus: avoid scheduling in interrupt context in vmbus_initiate_unload()

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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: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Vitaly Kuznetsov 2016-01-27 22:29:35 -08:00 committed by Greg Kroah-Hartman
parent 79fd8e7066
commit 415719160d
1 changed files with 43 additions and 1 deletions
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44
drivers/hv/channel_mgmt.c
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@ -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));
wait_for_completion(&vmbus_connection.unload_event);
/*
* 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();
}
/*