Re: [patch 17/59] PCI: prevent down_read when pci_devices is empty

Kumar Gala
2007-02-03T16:17:16Z

On Feb 2, 2007, at 8:35 PM, Chris Wright wrote:

> -stable review patch. If anyone has any objections, please let us
> know.
> ------------------

We just updated this for mainline to remove the printks. I'd prefer
to see that version of this patch go in.

- k

>
> From: Ard van Breemen <ard@telegraafnet.nl>
>
> The pci_find_subsys gets called very early by obsolete ide setup
> parameters.
> This is a bogus call since pci is not initialized yet, so the list
> is empty.
> But in the mean time, interrupts get enabled by down_read. This
> can result in
> a kernel panic when the irq controller gets initialized.
>
> This patch checks if the device list is empty before taking the
> semaphore, and
> hence will not enable irq's. Furthermore it will inform that it is
> called
> while pci_devices is empty as a reminder that the ide code needs to
> be fixed.
>
> The pci_get_subsys can get called in the same manner, and as such
> is patched
> in the same manner.
>
> [akpm@osdl.org: cleanups]
> Signed-off-by: Ard van Breemen <ard@telegraafnet.nl>
> Cc: Greg KH <greg@kroah.com>
> Signed-off-by: Andrew Morton <akpm@osdl.org>
> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
> Signed-off-by: Chris Wright <chrisw@sous-sol.org>
> ---
> This is the other half of the fix for bug #7505
>
> drivers/pci/search.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> --- linux-2.6.19.2.orig/drivers/pci/search.c
> +++ linux-2.6.19.2/drivers/pci/search.c
> @@ -193,6 +193,18 @@ static struct pci_dev * pci_find_subsys(
> struct pci_dev *dev;
>
> WARN_ON(in_interrupt());
> +
> + /*
> + * pci_find_subsys() can be called on the ide_setup() path, super-
> early
> + * in boot. But the down_read() will enable local interrupts, which
> + * can cause some machines to crash. So here we detect and flag
> that
> + * situation and bail out early.
> + */
> + if (unlikely(list_empty(&pci_devices))) {
> + printk(KERN_INFO "pci_find_subsys() called while pci_devices "
> + "is still empty\n");
> + return NULL;
> + }
> down_read(&pci_bus_sem);
> n = from ? from->global_list.next : pci_devices.next;
>
> @@ -259,6 +271,18 @@ pci_get_subsys(unsigned int vendor, unsi
> struct pci_dev *dev;
>
> WARN_ON(in_interrupt());
> +
> + /*
> + * pci_get_subsys() can potentially be called by drivers super-early
> + * in boot. But the down_read() will enable local interrupts, which
> + * can cause some machines to crash. So here we detect and flag
> that
> + * situation and bail out early.
> + */
> + if (unlikely(list_empty(&pci_devices))) {
> + printk(KERN_NOTICE "pci_get_subsys() called while pci_devices "
> + "is still empty\n");
> + return NULL;
> + }
> down_read(&pci_bus_sem);
> n = from ? from->global_list.next : pci_devices.next;
>
>
> --
> -
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