Re: [PATCH v3 01/16] PCI: dwc: Add pcie_cap field and helper in designware header

On 7/20/26 23:17, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Data race and logically flawed caching in dw_pcie_get_pcie_cap() due to unprotected read-modify-write and failure to cache 'not found' state.
> --
> 
> --- Patch [1]: [PATCH v3 01/16] PCI: dwc: Add pcie_cap field and helper in designware header ---
> commit ab22dc6f534d77b34df13c99dd929771547f5ff1
> Author: Hans Zhang <[email protected]>
> 
> PCI: dwc: Add pcie_cap field and helper in designware header
> 
> This commit adds a pcie_cap field to struct dw_pcie to cache the offset of
> the PCI Express Capability structure. It introduces dw_pcie_get_pcie_cap()
> to perform the capability search on the first call and cache the result.
> 
>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
>> --- a/drivers/pci/controller/dwc/pcie-designware.h
>> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> [ ... ]
>> @@ -829,6 +831,21 @@ static inline void dw_pcie_dbi_ro_wr_dis(struct dw_pcie *pci)
>>   	dw_pcie_writel_dbi(pci, reg, val);
>>   }
>>   
>> +/**
>> + * dw_pcie_get_pcie_cap() - Return cached PCIe Capability offset
>> + * @pci: DWC instance
>> + *
>> + * Finds and caches the offset of PCI_CAP_ID_EXP on first call.
>> + * Returns 0 if the capability is not present.
>> + */
>> +static inline u8 dw_pcie_get_pcie_cap(struct dw_pcie *pci)
>> +{
>> +	if (!pci->pcie_cap)
>> +		pci->pcie_cap = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> 
> [Severity: Medium]
> Will this repeatedly search the configuration space if the capability is
> not found? If dw_pcie_find_capability() returns 0 when the capability is
> missing, pci->pcie_cap will remain 0, causing the search to be repeated
> on every subsequent call instead of being cached.
> 
> Also, since this helper might be called concurrently by different threads,
> could the unprotected read and write to pci->pcie_cap cause a data race?
> 

Hi,

As mentioned in the previous reply, there is no need for us to worry 
about this.

https://lore.kernel.org/linux-pci/[email protected]/


Best regards,
Hans


>> +
>> +	return pci->pcie_cap;
>> +}
> 


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