linux-kernel - Re: [PATCH v5 8/9] PCI: Define scoped based management functions

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Message-ID: <6597275045fbf_267e82949d@iweiny-mobl.notmuch>
Date: Thu, 4 Jan 2024 13:46:56 -0800
From: Ira Weiny <ira.weiny@...el.com>
To: Dan Williams <dan.j.williams@...el.com>, Bjorn Helgaas
	<helgaas@...nel.org>
CC: Bjorn Helgaas <bhelgaas@...gle.com>, Ira Weiny <ira.weiny@...el.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>, Smita Koralahalli
	<Smita.KoralahalliChannabasappa@....com>, Shiju Jose <shiju.jose@...wei.com>,
	Yazen Ghannam <yazen.ghannam@....com>, Davidlohr Bueso <dave@...olabs.net>,
	Dave Jiang <dave.jiang@...el.com>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Ard
 Biesheuvel" <ardb@...nel.org>, <linux-efi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
	<linux-pci@...r.kernel.org>
Subject: Re: [PATCH v5 8/9] PCI: Define scoped based management functions

Dan Williams wrote:
> Bjorn Helgaas wrote:
> [..]
> > > ---
> > > PCI: Introduce cleanup helpers for device reference counts and locks
> > > 
> > > The "goto error" pattern is notorious for introducing subtle resource
> > > leaks. Use the new cleanup.h helpers for PCI device reference counts and
> > > locks.
> > > 
> > > Similar to the new put_device() and device_lock() cleanup helpers,
> > > __free(put_device) and guard(device), define the same for PCI devices,
> > > __free(pci_dev_put) and guard(pci_dev).  These helpers eliminate the
> > > need for "goto free;" and "goto unlock;" patterns. For example, A
> > > 'struct pci_dev *' instance declared as:
> > > 
> > > 	struct pci_dev *pdev __free(pci_dev_put) = NULL;
> > 
> > I see several similar __free() uses with NULL initializations in gpio,
> > but I think this idiom would be slightly improved if the __free()
> > function were more closely associated with the actual pci_dev_get():
> > 
> >   struct pci_dev *pdev __free(pci_dev_put) = pci_get_device(...);
> > 
> > Not always possible, I know, but easier to analyze when it is.
> 
> I tend to agree, but it does lead to some long lines, for example:
> 
> diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> index 4fd1f207c84e..549ba4b8294e 100644
> --- a/drivers/cxl/pci.c
> +++ b/drivers/cxl/pci.c
> @@ -975,15 +975,14 @@ static void cxl_cper_event_call(enum cxl_event_type ev_type,
>  				struct cxl_cper_event_rec *rec)
>  {
>  	struct cper_cxl_event_devid *device_id = &rec->hdr.device_id;
> -	struct pci_dev *pdev __free(pci_dev_put) = NULL;
>  	enum cxl_event_log_type log_type;
>  	struct cxl_dev_state *cxlds;
>  	unsigned int devfn;
>  	u32 hdr_flags;
>  
>  	devfn = PCI_DEVFN(device_id->device_num, device_id->func_num);
> -	pdev = pci_get_domain_bus_and_slot(device_id->segment_num,
> -					   device_id->bus_num, devfn);
> +	struct pci_dev *pdev __free(pci_dev_put) = pci_get_domain_bus_and_slot(
> +		device_id->segment_num, device_id->bus_num, devfn);
>  	if (!pdev)
>  		return;
>  
> ...so I think people are choosing the "... __free(x) = NULL;" style for
> code density readability.
> 

Also in this case we need devfn assigned first.

Is the above patch compliant with current style guidelines?

Or would it be better to do?

diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
index b14237f824cf..8a180c6abb67 100644
--- a/drivers/cxl/pci.c
+++ b/drivers/cxl/pci.c
@@ -975,15 +975,14 @@ static void cxl_cper_event_call(enum cxl_event_type ev_type,
                                struct cxl_cper_event_rec *rec)
 {
        struct cper_cxl_event_devid *device_id = &rec->hdr.device_id;
-       struct pci_dev *pdev __free(pci_dev_put) = NULL;
        enum cxl_event_log_type log_type;
        struct cxl_dev_state *cxlds;
-       unsigned int devfn;
+       unsigned int devfn = PCI_DEVFN(device_id->device_num, device_id->func_num);
+       struct pci_dev *pdev __free(pci_dev_put) = pci_get_domain_bus_and_slot(
+                                                       device_id->segment_num,
+                                                       device_id->bus_num, devfn);
        u32 hdr_flags;
 
-       devfn = PCI_DEVFN(device_id->device_num, device_id->func_num);
-       pdev = pci_get_domain_bus_and_slot(device_id->segment_num,
-                                          device_id->bus_num, devfn);
        if (!pdev)
                return;
 

Ira