linux-kernel - Re: ARM/gic-v4: deadlock occurred

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Date:   Mon, 15 Jul 2019 12:13:37 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Guoheyi <guoheyi@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        wanghaibin 00208455 <wanghaibin.wang@...wei.com>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>
Subject: Re: ARM/gic-v4: deadlock occurred

On 15/07/2019 11:43, Guoheyi wrote:
> 
> 
> On 2019/7/15 17:07, Marc Zyngier wrote:
>> On 15/07/2019 07:32, Guoheyi wrote:
>>> Hi Marc,
>>>
>>> The issue only occurs after applying the vlpi_map_rework patches, and we
>>> can see the patches only affect VM; it changes its_create_device() a
>>> little so it may affect host booting in some ways, so I took the lazy
>>> way to send it out for some insights.
>>>
>>> I am suspecting below code; if alloc_lpis == false, what will happen?
>> If !alloc_lpis, then we don't allocate the lpi_map, which is the
>> intended effect.
>>
>>> Anyway, I will investigate more on this.
>>>
>>>
>>> 	if  (alloc_lpis)  {
>>> 		lpi_map  =  its_lpi_alloc(nvecs,  &lpi_base,  &nr_lpis);
>>> 		if  (lpi_map)
>>> 			col_map  =  kcalloc(nr_lpis,  sizeof(*col_map),
>>> 					GFP_KERNEL);
>>> 	}  else  {
>>> 		col_map  =  kcalloc(nr_ites,  sizeof(*col_map),  GFP_KERNEL);
>>> 		nr_lpis  =  0;
>>> 		lpi_base  =  0;
>>> 	}
>>> 	if  (its->is_v4)
>>> 		vlpi_map  =  kcalloc(nr_lpis,  sizeof(*vlpi_map),  GFP_KERNEL);
>>>
>>> 	if  (!dev  ||  !itt  ||   !col_map  ||  (!lpi_map  &&  alloc_lpis)  ||
>>> 	(!vlpi_map  &&  its->is_v4))  {
>>> 		kfree(dev);
>>> 		kfree(itt);
>>> 		kfree(lpi_map);
>>> 		kfree(col_map);
>>> 		kfree(vlpi_map);
>>> 		return  NULL;
>>> 	}
>> How does this relate to the patch posted in this discussion? The
>> proposed changes turn the locking from a mutex into a raw_spinlock.
> 
> I'm testing the patchset in 
> https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/vlpi-map-rework, 
> not only the patch posted in the mail directly. The first patch 
> *"**irqchip/gic-v3-its: Make vlpi_map allocations atomic" works well in 
> our internal tree, and my new testing is against the other 3 patches in 
> your vlpi-map-rework branch, as I promised. I'm sorry if I didn't state 
> this clearly.

Ah, I had completely forgot about this branch. As I said, it is
completely untested. I'll see if I can get some brain bandwidth in the
next couple of weeks to get back to it...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...