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

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Message-ID: <7340a27e-67c1-c0c3-9304-77710dc44f7f@loongson.cn>
Date: Wed, 24 Jul 2024 09:58:16 +0800
From: Hongchen Zhang <zhanghongchen@...ngson.cn>
To: Ethan Zhao <haifeng.zhao@...ux.intel.com>,
 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

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


-- 
Best Regards
Hongchen Zhang