linux-kernel - Re: [patch 17/59] PCI: prevent down_read when pci

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Message-Id: <5EFB4FBE-A880-4078-A5A1-74F4C22FF93A@kernel.crashing.org>
Date:	Sat, 3 Feb 2007 10:16:20 -0600
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	stable@...nel.org, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [patch 17/59] PCI: prevent down_read when pci_devices is empty


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@...egraafnet.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@...l.org: cleanups]
> Signed-off-by: Ard van Breemen <ard@...egraafnet.nl>
> Cc: Greg KH <greg@...ah.com>
> Signed-off-by: Andrew Morton <akpm@...l.org>
> Signed-off-by: Linus Torvalds <torvalds@...l.org>
> Signed-off-by: Chris Wright <chrisw@...s-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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