Re: [PATCH 0/37] PCI/MSI: Enforce explicit IRQ vector management by removing devres auto-free

Andy Shevchenko
2026-02-23T15:51:37Z

On Mon, Feb 23, 2026 at 5:32 PM Shawn Lin <shawn.lin@rock-chips.com> wrote:
>
> This patch series addresses a long-standing design issue in the PCI/MSI
> subsystem where the implicit, automatic management of IRQ vectors by
> the devres framework conflicts with explicit driver cleanup, creating
> ambiguity and potential resource management bugs.
>
> ==== The Problem: Implicit vs. Explicit Management ====
> Historically, `pcim_enable_device()` not only manages standard PCI resources
> (BARs) via devres but also implicitly triggers automatic IRQ vector management
> by setting a flag that registers `pcim_msi_release()` as a cleanup action.
>
> This creates an ambiguous ownership model. Many drivers follow a pattern of:
> 1. Calling `pci_alloc_irq_vectors()` to allocate interrupts.
> 2. Also calling `pci_free_irq_vectors()` in their error paths or remove routines.
>
> When such a driver also uses `pcim_enable_device()`, the devres framework may
> attempt to free the IRQ vectors a second time upon device release, leading to
> a double-free. Analysis of the tree shows this hazardous pattern exists widely,
> while 35 other drivers correctly rely solely on the implicit cleanup.

Is this confirmed? What I read from the cover letter, this series was
only compile-tested, so how can you prove the problem exists in the
first place?

> ==== The Solution: Making Management Explicit ====
> This series enforces a clear, predictable model:
> 1. New Managed API (Patch 1/37): Introduces pcim_alloc_irq_vectors() and
> pcim_alloc_irq_vectors_affinity(). Drivers that desire devres-managed IRQ
> vectors should use these functions, which set the is_msi_managed flag and
> ensure automatic cleanup.
> 2. Patches 2 through 36 convert each driver that uses pcim_enable_device() alongside
> pci_alloc_irq_vectors() and relies on devres for IRQ vector cleanup to instead
> make an explicit call to pcim_alloc_irq_vectors().
> 3. Core Change (Patch 37/37): With the former cleanup, now modifies pcim_setup_msi_release()
> to check only the is_msi_managed flag. This decouples automatic IRQ cleanup from
> pcim_enable_device(). IRQ vectors allocated via pci_alloc_irq_vectors*()
> are now solely the driver's responsibility to free with pci_free_irq_vectors().
>
> With these changes, we clear ownership model: Explicit resource management eliminates
> ambiguity and follows the "principle of least surprise." New drivers choose one model and
> be consistent.
> - Use `pci_alloc_irq_vectors()` + `pci_free_irq_vectors()` for explicit control.
> - Use `pcim_alloc_irq_vectors()` for devres-managed, automatic cleanup.

Have you checked previous attempts? Why is your series better than those?

> ==== Testing And Review ====
> 1. This series is only compiled test with allmodconfig.
> 2. Given the substantial size of this patch series, I have structured the mailing
> to facilitate efficient review. The cover letter, the first patch and the last one will be sent
> to all relevant mailing lists and key maintainers to ensure broad visibility and
> initial feedback on the overall approach. The remaining subsystem-specific patches
> will be sent only to the respective subsystem maintainers and their associated
> mailing lists, reducing noise.

--
With Best Regards,
Andy Shevchenko