linux-kernel - Re: [PATCHv2] PCI: Add pci

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Date:   Thu, 20 Aug 2020 16:55:49 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     George Cherian <george.cherian@...vell.com>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-pci@...r.kernel.org, bhelgaas@...gle.com, arnd@...db.de,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCHv2] PCI: Add pci_iounmap

[+cc Michael, author of 66eab4df288a ("lib: add GENERIC_PCI_IOMAP")]

On Thu, Aug 20, 2020 at 10:33:06AM +0530, George Cherian wrote:
> In case if any architecture selects CONFIG_GENERIC_PCI_IOMAP and not
> CONFIG_GENERIC_IOMAP, then the pci_iounmap function is reduced to a NULL
> function. Due to this the managed release variants or even the explicit
> pci_iounmap calls doesn't really remove the mappings.
> 
> This issue is seen on an arm64 based system. arm64 by default selects
> only CONFIG_GENERIC_PCI_IOMAP and not CONFIG_GENERIC_IOMAP from this
> 'commit cb61f6769b88 ("ARM64: use GENERIC_PCI_IOMAP")'
> 
> Simple bind/unbind test of any pci driver using pcim_iomap/pci_iomap,
> would lead to the following error message after long hour tests
> 
> "allocation failed: out of vmalloc space - use vmalloc=<size> to
> increase size."
> 
> Signed-off-by: George Cherian <george.cherian@...vell.com>
> ---
> * Changes from v1
> 	- Fix the 0-day compilation error.
> 	- Mark the lib/iomap pci_iounmap call as weak incase 
> 	  if any architecture have there own implementation.
> 
>  include/asm-generic/io.h |  4 ++++
>  lib/pci_iomap.c          | 10 ++++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> index dabf8cb7203b..5986b37226b7 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -915,12 +915,16 @@ static inline void iowrite64_rep(volatile void __iomem *addr,
>  struct pci_dev;
>  extern void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long max);
>  
> +#ifdef CONFIG_GENERIC_PCI_IOMAP
> +extern void pci_iounmap(struct pci_dev *dev, void __iomem *p);
> +#else
>  #ifndef pci_iounmap
>  #define pci_iounmap pci_iounmap
>  static inline void pci_iounmap(struct pci_dev *dev, void __iomem *p)
>  {
>  }
>  #endif
> +#endif /* CONFIG_GENERIC_PCI_IOMAP */
>  #endif /* CONFIG_GENERIC_IOMAP */
>  
>  /*
> diff --git a/lib/pci_iomap.c b/lib/pci_iomap.c
> index 2d3eb1cb73b8..ecd1eb3f6c25 100644
> --- a/lib/pci_iomap.c
> +++ b/lib/pci_iomap.c
> @@ -134,4 +134,14 @@ void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long maxlen)
>  	return pci_iomap_wc_range(dev, bar, 0, maxlen);
>  }
>  EXPORT_SYMBOL_GPL(pci_iomap_wc);
> +
> +#ifndef CONFIG_GENERIC_IOMAP
> +#define pci_iounmap pci_iounmap
> +void __weak pci_iounmap(struct pci_dev *dev, void __iomem *addr);
> +void __weak pci_iounmap(struct pci_dev *dev, void __iomem *addr)
> +{
> +	iounmap(addr);
> +}
> +EXPORT_SYMBOL(pci_iounmap);
> +#endif

I completely agree that this looks like a leak that needs to be fixed.

But my head hurts after trying to understand pci_iomap() and
pci_iounmap().  I hate to add even more #ifdefs here.  Can't we
somehow rationalize this and put pci_iounmap() next to pci_iomap()?

66eab4df288a ("lib: add GENERIC_PCI_IOMAP") moved pci_iomap() from
lib/iomap.c to lib/pci_iomap.c, but left pci_iounmap() in lib/iomap.c.
There must be some good reason why they're separated, but I don't know
what it is.

>  #endif /* CONFIG_PCI */
> -- 
> 2.25.1
>