linux-kernel - Re: [patch V2 05/10] PCI/MSI: Switch to MSI descriptor locking to guard()

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Message-ID: <87ldt86cjj.ffs@tglx>
Date: Thu, 13 Mar 2025 18:55:12 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: LKML <linux-kernel@...r.kernel.org>, Marc Zyngier <maz@...nel.org>, Bjorn
 Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org, Peter Zijlstra
 <peterz@...radead.org>, Nishanth Menon <nm@...com>, Dhruva Gole
 <d-gole@...com>, Tero Kristo <kristo@...nel.org>, Santosh Shilimkar
 <ssantosh@...nel.org>, Logan Gunthorpe <logang@...tatee.com>, Dave Jiang
 <dave.jiang@...el.com>, Jon Mason <jdmason@...zu.us>, Allen Hubbe
 <allenbh@...il.com>, ntb@...ts.linux.dev, Michael Kelley
 <mhklinux@...look.com>, Wei Liu <wei.liu@...nel.org>, Haiyang Zhang
 <haiyangz@...rosoft.com>, linux-hyperv@...r.kernel.org, Wei Huang
 <wei.huang2@....com>, Manivannan Sadhasivam
 <manivannan.sadhasivam@...aro.org>, "James E.J. Bottomley"
 <James.Bottomley@...senPartnership.com>, "Martin K. Petersen"
 <martin.petersen@...cle.com>, linux-scsi@...r.kernel.org, Jonathan Cameron
 <Jonathan.Cameron@...ei.com>
Subject: Re: [patch V2 05/10] PCI/MSI: Switch to MSI descriptor locking to
 guard()

On Thu, Mar 13 2025 at 15:50, Jonathan Cameron wrote:
>> +	guard(msi_descs_lock)(&dev->dev);
>> +	int ret = __msix_setup_interrupts(dev, entries, nvec, masks);
>> +	if (ret)
>> +		pci_free_msi_irqs(dev);
>
> It's not immediately obvious what this is undoing (i.e. where the alloc
> is).  I think it is at least mostly the pci_msi_setup_msi_irqs in
> __msix_setup_interrupts

It's a universal cleanup for all possible error cases.

> Why not handle the error in __msix_setup_interrupts and make that function
> side effect free.  Does require gotos but in a function that isn't
> doing any cleanup magic so should be fine.

I had the gotos first and then hated them. But you are right, it's better
to have them than having the magic clean up at the call site.

I'll fold the delta patch below.

Thanks,

        tglx
---
--- a/drivers/pci/msi/msi.c
+++ b/drivers/pci/msi/msi.c
@@ -671,19 +671,23 @@ static int __msix_setup_interrupts(struc
 	int ret = msix_setup_msi_descs(dev, entries, nvec, masks);

 	if (ret)
-		return ret;
+		goto fail;

 	ret = pci_msi_setup_msi_irqs(dev, nvec, PCI_CAP_ID_MSIX);
 	if (ret)
-		return ret;
+		goto fail;

 	/* Check if all MSI entries honor device restrictions */
 	ret = msi_verify_entries(dev);
 	if (ret)
-		return ret;
+		goto fail;

 	msix_update_entries(dev, entries);
 	return 0;
+
+fail:
+	pci_free_msi_irqs(dev);
+	return ret;
 }

 static int msix_setup_interrupts(struct pci_dev *dev, struct msix_entry *entries,
@@ -693,10 +697,7 @@ static int msix_setup_interrupts(struct
 		affd ? irq_create_affinity_masks(nvec, affd) : NULL;

 	guard(msi_descs_lock)(&dev->dev);
-	int ret = __msix_setup_interrupts(dev, entries, nvec, masks);
-	if (ret)
-		pci_free_msi_irqs(dev);
-	return ret;
+	return __msix_setup_interrupts(dev, entries, nvec, masks);
 }

 /**