linux-kernel - Re: [PATCH v3] PCI: pci_call_probe: call local_pci

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Message-ID: <670927f1-42d8-40bc-bd79-55e178bd907a@linux.intel.com>
Date: Wed, 24 Jul 2024 10:47:04 +0800
From: Ethan Zhao <haifeng.zhao@...ux.intel.com>
To: Hongchen Zhang <zhanghongchen@...ngson.cn>,
 Markus Elfring <Markus.Elfring@....de>, Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Alex Belits <abelits@...vell.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Nitesh Narayan Lal <nitesh@...hat.com>,
 Frederic Weisbecker <frederic@...nel.org>, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
 stable@...r.kernel.org, Huacai Chen <chenhuacai@...ngson.cn>
Subject: Re: [PATCH v3] PCI: pci_call_probe: call local_pci_probe() when
 selected cpu is offline

On 7/24/2024 9:58 AM, Hongchen Zhang wrote:
> Hi Ethan,
> On 2024/7/22 PM 3:39, Ethan Zhao wrote:
>>
>> On 6/13/2024 3:42 PM, Hongchen Zhang wrote:
>>> Call work_on_cpu(cpu, fn, arg) in pci_call_probe() while the argument
>>> @cpu is a offline cpu would cause system stuck forever.
>>>
>>> This can be happen if a node is online while all its CPUs are
>>> offline (We can use "maxcpus=1" without "nr_cpus=1" to reproduce it).
>>>
>>> So, in the above case, let pci_call_probe() call local_pci_probe()
>>> instead of work_on_cpu() when the best selected cpu is offline.
>>>
>>> Fixes: 69a18b18699b ("PCI: Restrict probe functions to housekeeping 
>>> CPUs")
>>> Cc: <stable@...r.kernel.org>
>>> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
>>> Signed-off-by: Hongchen Zhang <zhanghongchen@...ngson.cn>
>>> ---
>>> v2 -> v3: Modify commit message according to Markus's suggestion
>>> v1 -> v2: Add a method to reproduce the problem
>>> ---
>>>   drivers/pci/pci-driver.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>>> index af2996d0d17f..32a99828e6a3 100644
>>> --- a/drivers/pci/pci-driver.c
>>> +++ b/drivers/pci/pci-driver.c
>>> @@ -386,7 +386,7 @@ static int pci_call_probe(struct pci_driver 
>>> *drv, struct pci_dev *dev,
>>>           free_cpumask_var(wq_domain_mask);
>>>       }
>>> -    if (cpu < nr_cpu_ids)
>>
>> Why not choose the right cpu to callwork_on_cpu() ? the one that is 
>> online. Thanks, Ethan
> Yes, let housekeeping_cpumask() return online cpu is a good idea, but 
> it may be changed by command line. so the simplest way is to call 
> local_pci_probe when the best selected cpu is offline.

Hmm..... housekeeping_cpumask() should never return offline CPU, so
I guess you didn't hit issue with the CPU isolation, but the following
code seems not good.

...

if (node < 0 || node >= MAX_NUMNODES || !node_online(node) ||
         pci_physfn_is_probed(dev)) {
         cpu = nr_cpu_ids;
     } else {

....

perhaps you could change the logic there and fix it  ?

Thanks
Ethan



>>
>>> +    if ((cpu < nr_cpu_ids) && cpu_online(cpu))
>>>           error = work_on_cpu(cpu, local_pci_probe, &ddi);
>>>       else
>>>           error = local_pci_probe(&ddi);
>
>