RE: Problems with EDAC coexisting with BIOS

["Doug Thompson" <dthompson@lnxi.com>]

On Fri, 2006-04-21 at 21:32 +0000, "Gross, Mark"  wrote:
> 
> >-----Original Message-----
> >From: Doug Thompson [mailto:dthompson@lnxi.com]
> >Sent: Friday, April 21, 2006 1:57 PM
> >To: Gross, Mark
> >Cc: Ong, Soo Keong; Carbonari, Steven; Wang, Zhenyu Z; bluesmoke-
> >devel@lists.sourceforge.net; linux-kernel@vger.kernel.org
> >Subject: Re: Problems with EDAC coexisting with BIOS
> >
> >Mark thanks for the informaton on this.
> >
> >Now the e752x_edac.c driver contains no direct calls to panic within
> >itself. The edac_mc.c 'core' piece does, but only calls that if an UE
> >error is found and panic on UE is enabled. (The other is a PCI parity
> >panic, but doesn't effect this path). It might be possible that since
> >the hidden register was now hidden, the retrieval function returns some
> >garbage which falsely triggers the panic by the core.
> 
> The problem is that once the BIOS SMI re-hides the device reading from
> the chipset error registers returns 0xFFFFFFFF.

Ok so the panic is caused by the driver because the UE bit is a one
(somewhere in the 32-bit field), and then informs the CORE driver of the
false positive UE event, which does the panic trigger. I follow the
logic now.

The question then comes up: how to determine if the system has the
hidden register feature.

You mentioned that the probe should be refactored to look for this all
ones return value as such an indicator, is that correct?

But there is a window that the register is unhidden, the probe runs,
detects the hardware it is looking at and registers itself. Then later
the window closes, the register is hidden again and the panic can
reoccurr as above. Thus, a check needs to be made in the poll operation
for the all ones return value, notify the log of this situtation,
shutdown future polling of this hardware and basicly become a no-op poll
operation.

Does that fix cover the issue as you have discovered it? Or is there
more, or another fix you see?

doug t



> 
> >
> >I would like to see the panic output and stack trace to see where that
> >panic came from. It might have come from the PCI device access subsytem
> >when it was trying to access the now hidden register.
> >
> >can you post that panice information?
> 
> Yes, but the edac_mc.c call to panic doesn't drop any data to the
> console.
> The following is the output from an instrumentation we did to the EDAC
> that went into RHEL4-U3 :
> 
> INIT: version 2.85 booting
>                 Welcome to Red Hat Enterprise Linux AS
>                 Press 'I' to enter interactive startup.
> Starting udev:  [  OK  ]
> Initializing hardware...  storage network audioIn probe1, before write
> E752X_DEVPRES1 = 0x10
> In probe1, after write
> E752X_DEVPRES1 = 0x30
> 
> Snip .....
> 
> Configuring kernel parameters:  [  OK  ]
> Setting clock  (localtime): Sun Mar 12 00:52:17 PST 2006 [  OK  ]
> Setting hostname localhost.localdomain:  [  OK  ]
> Checking root filesystem
> [/sbin/fsck.ext3 (1) -- /] fsck.ext3 -a /dev/sda1
> /: clean, 365954/8830976 files, 2357630/17657443 blocks
> [  OK  ]
> Remounting root filesystem in read-write mode:  [  OK  ]
> No devices found
> No Software RAID disks
> Setting up Logical Volume ManageE752X_DEVPRES1 = 0x10
> ment: E752X_DEVPRES1 = 0x10
> Kernel panic - not syncing: MC0: Uncorrected Error
> 
> that's all you get, no stack trace.
> 
> The EX752C_DEVPRES1 = ... debug statements came from sprinkling call to
> the following debug function we instrumented into the EDAC driver code.
> 
> static void print_error_info(struct pci_dev *pdev) 
> {
>   u8 stat8;
>   pci_read_config_byte(pdev, E752X_DEVPRES1, &stat8);
>   printk(KERN_EMERG "E752X_DEVPRES1 = 0x%02X\n", stat8);
> }
> 


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