linux-kernel - Re: [PATCH v2 3/3] Drivers: hv: vmbus: setup irq after synic is initialized

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Date:	Tue, 12 May 2015 18:34:25 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	Haiyang Zhang <haiyangz@...rosoft.com>,
	"devel\@linuxdriverproject.org" <devel@...uxdriverproject.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	"Dan Carpenter" <dan.carpenter@...cle.com>
Subject: Re: [PATCH v2 3/3] Drivers: hv: vmbus: setup irq after synic is initialized

KY Srinivasan <kys@...rosoft.com> writes:

>> -----Original Message-----
>> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
>> Sent: Tuesday, April 21, 2015 9:22 AM
>> To: KY Srinivasan
>> Cc: Haiyang Zhang; devel@...uxdriverproject.org; linux-
>> kernel@...r.kernel.org; Dexuan Cui; Dan Carpenter
>> Subject: [PATCH v2 3/3] Drivers: hv: vmbus: setup irq after synic is initialized
>> 
>> vmbus_isr() uses synic pages which are being setup in hv_synic_alloc(), we
>> need to register this irq handler only after we allocate all the required
>> pages.
>
> Why? Until we tell the hypervisor to route the vmbus interrupts on the specified vector,
> no vmbus interrupts will be delivered and this is done in the function hv_synic_init().
> So, the only requirement here is that all of the irq plumbing and allocations be done 
> before we enable the synthetic interrupt controller and register the vector with the
> hypervisor. What am I missing.

I should have made it clearer that I'm not fixing a bug here, it just
looks logical to me to put synic pages allocation (hv_synic_alloc())
before we register vmbus_isr() handler which uses these pages. You're
absolutely right and this handler won't be executed with unallocated
pages now, this patch was rather future-proof.


>
> Regards,
>
> K. Y
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  drivers/hv/vmbus_drv.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
>> index cf20400..e922804 100644
>> --- a/drivers/hv/vmbus_drv.c
>> +++ b/drivers/hv/vmbus_drv.c
>> @@ -822,11 +822,12 @@ static int vmbus_bus_init(int irq)
>>  	if (ret)
>>  		goto err_cleanup;
>> 
>> -	hv_setup_vmbus_irq(vmbus_isr);
>> -
>>  	ret = hv_synic_alloc();
>>  	if (ret)
>>  		goto err_alloc;
>> +
>> +	hv_setup_vmbus_irq(vmbus_isr);
>> +
>>  	/*
>>  	 * Initialize the per-cpu interrupt state and
>>  	 * connect to the host.
>> --
>> 1.9.3

-- 
  Vitaly
--
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