Re: [PATCH 2/3] staging: ccree: Convert to devm_ioremap_resource for map, unmap

[Suniel Mahesh]

On Friday 28 July 2017 01:18 AM, Dan Carpenter wrote:
> On Thu, Jul 27, 2017 at 05:27:33PM +0300, Gilad Ben-Yossef wrote:
>> +	new_drvdata->cc_base = devm_ioremap_resource(&plat_dev->dev,
>> +						     req_mem_cc_regs);
>> +	if (IS_ERR(new_drvdata->cc_base)) {
>> +		rc = PTR_ERR(new_drvdata->cc_base);
>>  		goto init_cc_res_err;
>                 ^^^^^^^^^^^^^^^^^^^^
> (This code was in the original and not introduced by the patch.)

Hi Dan, the above lines of code were not in the original except 
"goto init_cc_res_err;" which was doing the error handling at different
places.

This patch has added those first three lines. I was constantly checking the latest
linux-next and staging-testing / next git trees. 
 
> 
> Ideally, the goto name should say what the goto does.  In this case it
> does everything.  Unfortunately trying to do everything is very
> complicated so obviously the error handling is going to be full of bugs.
> 
> The first thing the error handling does is:
> 
> 	ssi_aead_free(new_drvdata);
> 
> But this function assumes that if new_drvdata->aead_handle is non-NULL
> then that means we have called:
> 
> 	INIT_LIST_HEAD(&aead_handle->aead_list);
> 
> That assumption is false if the aead_handle->sram_workspace_addr
> allocation fails.  It can't actually fail in the current code...  So
> that's good, I suppose.  Reviewing this code is really hard, because I
> have to jump back and forth through several functions in different
> files.
> 
> Moving on two the second error handling function:
> 
> 	ssi_hash_free(new_drvdata);
> 
> This one has basically the same assumption that if ->hash_handle is
> allocated that means we called:
> 
> 	INIT_LIST_HEAD(&hash_handle->hash_list);
> 
> That assumption is not true if ssi_hash_init_sram_digest_consts(drvdata);
> fails.  That function can fail in real life.  Except the the error
> handling in ssi_hash_alloc() sets ->hash_handle to NULL.  So the bug is
> just a leak and not a crashing bug.
> 
> I've reviewed the first two lines of the error handling just to give a
> feel for how complicated "do everything" style error handling is to
> review.
> 
> The better way to do error handling is:
> 1) Only free things which have been allocated.
> 2) The unwind code should mirror the wind up code.
> 3) Every allocation function should have a free function.
> 4) Label names should tell you what the goto does.
> 5) Use direct returns and literals where possible.
> 6) Generally it's better to keep the error path and the success path
>    separate.
> 7) Do error handling as opposed to success handling.
> 
> 	one = alloc();
> 	if (!one)
> 		return -ENOMEM;
> 	if (foo) {
> 		two = alloc();
> 		if (!two) {
> 			ret = -ENOMEM;
> 			goto free_one;
> 		}
> 	}
> 	three = alloc();
> 	if (!three) {
> 		ret = -ENOMEM;
> 		goto free_two;
> 	}
> 	...
> 
> 	return 0;
> 
> free_two:
> 	if (foo)
> 		free(two);
> free_one:
> 	free(one);
> 
> 	return ret;
> 
> This style of error handling is easier to review.  You only need to
> remember the most recent thing that you have allocated.  You can tell
> from the goto that it frees it so you don't have to scroll to the
> bottom of the function or jump to a different file.

I understand, its make sense, may be we should come up with something 
better and simpler.

Thanks
Suniel

> 
> regards,
> dan carpenter
> 
>