Re: [PATCH] cxl: Perform NULL check for 'cxl_afu *' at various places in cxl

[Vaibhav Jain <vaibhav@linux.vnet.ibm.com>]

Thanks for looking into this patch Andrew,

Andrew Donnellan <andrew.donnellan@au1.ibm.com> writes:

> On 08/03/18 21:05, Vaibhav Jain wrote:
>> It is possible for a CXL card to have a valid PSL but no valid
>> AFUs. When this happens we have a valid instance of 'struct cxl'
>> representing the adapter but with its member 'struct cxl_afu *cxl[]'
>> as empty. Unfortunately at many placed within cxl code (especially
>> during an EEH) the elements of this array are passed on to various
>> other cxl functions. Which may result in kernel oops/panic when this
>> 'struct cxl_afu *' is dereferenced.
>> 
>> So this patch puts a NULL check at the beginning of various cxl
>> functions that accept 'struct cxl_afu *' as a formal argument and are
>> called from with a loop of the form:
>> 
>>         for (i = 0; i < adapter->slices; i++) {
>>         	   	afu = adapter->afu[i];
>> 		/* call some function with 'afu' */
>> 	}
>
> Surely in this case adapter->slices should be 0?
Not necessarily, as adapter->slice doesnt take into account AFUs that
fail to init. I saw this issue in one specific case were the only slice
on the card had issued with the AFU descriptor caused CXL init of that
AFU to fail.

>
> We might still need to harden for other cases...
Yes we may need some more hardening especially in our AFU descriptor
parsing code.

-- 
Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.