linux-kernel - Re: [PATCH v4 2/4] PCI: Fix serious bug when sizing bridges with additional size

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Date:   Thu, 25 Apr 2019 08:33:56 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "corbet@....net" <corbet@....net>
Subject: Re: [PATCH v4 2/4] PCI: Fix serious bug when sizing bridges with
 additional size

On Wed, Apr 17, 2019 at 02:16:50PM +0000, Nicholas Johnson wrote:
> Change find_free_bus_resource function to not skip assigned resources
> with non-null parent.
> 
> Add checks in pbus_size_io and pbus_size_mem to return success if
> resource returned from find_free_bus_resource is already allocated.
> 
> This avoids pbus_size_io and pbus_size_mem returning error code to
> __pci_bus_size_bridges when a resource has been successfully assigned in
> a previous pass. This fixes the existing behaviour where space for a
> resource could be reserved multiple times in different parent bridge
> windows. This also greatly reduces the number of failed BAR messages in
> dmesg when Linux assigns resources.

A concrete example for this would be helpful, e.g., a dmesg log
showing space for a single resource being reserved multiple times in
different windows.  This is probably too big for a commit log, so you
could open an issue at bugzilla.kernel.org, attach the complete dmesg
logs there, maybe include snippets here, and include the URL for more
details.

General comment: in English text, include "()" on function names as a
hint to the reader, e.g., you can write

  Change find_free_bus_resource() to not ...

instead of

  Change find_free_bus_resource function ...

> Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
> ---
>  drivers/pci/setup-bus.c | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index a1ca8a11f..5b9ee9945 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -752,11 +752,17 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
>  	}
>  }
>  
> -/* Helper function for sizing routines: find first available
> -   bus resource of a given type. Note: we intentionally skip
> -   the bus resources which have already been assigned (that is,
> -   have non-NULL parent resource). */
> -static struct resource *find_free_bus_resource(struct pci_bus *bus,
> +/*
> + * Helper function for sizing routines: find first bus resource of a given
> + * type. Note: we do not skip the bus resources which have already been
> + * assigned (r->parent != NULL). This is because a resource that is already
> + * assigned (nothing more to be done) will be indistinguishable from one that
> + * failed due to lack of space if we skip assigned resources. If the caller
> + * function cannot tell the difference then it might try to place the
> + * resources in a different window, doubling up on resources or causing
> + * unforeseeable issues.
> + */
> +static struct resource *find_bus_resource_of_type(struct pci_bus *bus,
>  			 unsigned long type_mask, unsigned long type)
>  {
>  	int i;
> @@ -765,7 +771,7 @@ static struct resource *find_free_bus_resource(struct pci_bus *bus,
>  	pci_bus_for_each_resource(bus, r, i) {
>  		if (r == &ioport_resource || r == &iomem_resource)
>  			continue;
> -		if (r && (r->flags & type_mask) == type && !r->parent)
> +		if (r && (r->flags & type_mask) == type)
>  			return r;
>  	}
>  	return NULL;
> @@ -863,14 +869,16 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
>  		resource_size_t add_size, struct list_head *realloc_head)
>  {
>  	struct pci_dev *dev;
> -	struct resource *b_res = find_free_bus_resource(bus, IORESOURCE_IO,
> -							IORESOURCE_IO);
> +	struct resource *b_res = find_bus_resource_of_type(bus, IORESOURCE_IO,
> +					IORESOURCE_IO);
>  	resource_size_t size = 0, size0 = 0, size1 = 0;
>  	resource_size_t children_add_size = 0;
>  	resource_size_t min_align, align;
>  
>  	if (!b_res)
>  		return;
> +	if (b_res->parent)
> +		return;
>  
>  	min_align = window_alignment(bus, IORESOURCE_IO);
>  	list_for_each_entry(dev, &bus->devices, bus_list) {
> @@ -975,7 +983,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
>  	resource_size_t min_align, align, size, size0, size1;
>  	resource_size_t aligns[18];	/* Alignments from 1Mb to 128Gb */
>  	int order, max_order;
> -	struct resource *b_res = find_free_bus_resource(bus,
> +	struct resource *b_res = find_bus_resource_of_type(bus,
>  					mask | IORESOURCE_PREFETCH, type);
>  	resource_size_t children_add_size = 0;
>  	resource_size_t children_add_align = 0;
> @@ -983,6 +991,8 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
>  
>  	if (!b_res)
>  		return -ENOSPC;
> +	if (b_res->parent)
> +		return 0;
>  
>  	memset(aligns, 0, sizeof(aligns));
>  	max_order = 0;
> -- 
> 2.20.1
>