linux-kernel - Re: [PATCH v2 1/2] PCI: Fix issue with "pci=disable_acs

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Message-ID: <20190412203256.GF141472@google.com>
Date:   Fri, 12 Apr 2019 15:32:56 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v2 1/2] PCI: Fix issue with "pci=disable_acs_redir"
 parameter being ignored

On Wed, Apr 10, 2019 at 03:05:31PM -0600, Logan Gunthorpe wrote:
> In most cases, kmalloc will not be available early in boot when
> pci_setup() is called. Thus, the kstrdup call that was added to fix the
> __initdata bug with the disable_acs_redir parameter usually returns
> NULL. Thus the parameter is discarded and it does not take into effect.
> 
> To fix this, we store the string that's in initdata until a initcall
> function can allocate the memory appropriately. This way we
> don't need any additional static memory.
> 
> Fixes: d2fd6e81912a ("PCI: Fix __initdata issue with "pci=disable_acs_redir" parameter")
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>

Applied to for-linus for v5.1, thanks, Logan!

> ---
>  drivers/pci/pci.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7c1b362f599a..766f5779db92 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -6262,8 +6262,7 @@ static int __init pci_setup(char *str)
>  			} else if (!strncmp(str, "pcie_scan_all", 13)) {
>  				pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
>  			} else if (!strncmp(str, "disable_acs_redir=", 18)) {
> -				disable_acs_redir_param =
> -					kstrdup(str + 18, GFP_KERNEL);
> +				disable_acs_redir_param = str + 18;
>  			} else {
>  				printk(KERN_ERR "PCI: Unknown option `%s'\n",
>  						str);
> @@ -6274,3 +6273,19 @@ static int __init pci_setup(char *str)
>  	return 0;
>  }
>  early_param("pci", pci_setup);
> +
> +/*
> + * 'disable_acs_redir_param' is initialized in pci_setup(), above, to point
> + * to data in the __initdata section which will be freed after the init
> + * sequence is complete. We can't allocate memory in pci_setup() because some
> + * architectures do not have any memory allocation service available during
> + * an early_param() call. So we allocate memory and copy the variable here
> + * before the init section is freed.
> + */
> +static int __init pci_realloc_setup_params(void)
> +{
> +	disable_acs_redir_param = kstrdup(disable_acs_redir_param, GFP_KERNEL);
> +
> +	return 0;
> +}
> +pure_initcall(pci_realloc_setup_params);
> -- 
> 2.20.1
>