BUG in 2.6.26-rc8 interrupt handling

["Becker Stefan (Nokia-D/Salo)" <Stefan.Becker@nokia.com>]

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Hi,

[I'm not subscribed to this list, so please CC: me]

[Subject has been changed, please read the rest of the thread for all 
the details]

On my AthlonXP single CPU laptop I experience random lockups when I 
access the external USB harddrive with kernels >2.6.23. The problem 
doesn't appear with 2.6.23.

Debugging revealed that a routine was called twice that takes a 
spinlock. But this actually shouldn't happen, because the function 
should only be invoked with interrupts disabled. A little more debugging 
revealed that apparently sometimes interrupts are enabled when the USB 
HCD interrupt handlers are called, although they are registered with 
IRQF_DISABLED.

With the attached patch ontop of 2.6.26-rc8 I get these messages:

kernel: USB_HCD_IRQ interrupts disabled 14206 enabled 6289
kernel: USB_HCD_IRQ interrupts disabled 14761 enabled 6290
kernel: USB_HCD_IRQ interrupts disabled 14761 enabled 6291

I also attached the contents from /proc/interrupts from the machine.

Any ideas what could be wrong or any suggestions in which direction I 
should continue debugging?

Regards,

	Stefan

---
Stefan Becker   Nokia-TP/Salo            Senior Specialist, EE SW
E-Mail: Stefan.Becker@nokia.com          SMS: 4871554@???.??
Office: +358-7180-71554                  FAX: +358-7180-44751
GSM   : +358-50-4871554

[-- Attachment #2: usb-hcd-interrupts.patch --]
[-- Type: text/plain, Size: 673 bytes --]

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 09a53e7..5814c5a 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1686,6 +1686,18 @@ irqreturn_t usb_hcd_irq (int irq, void *__hcd)
 	struct usb_hcd		*hcd = __hcd;
 	int			start = hcd->state;
 
+#ifdef DEBUG
+	static unsigned int _enabled  = 0;
+	static unsigned int _disabled = 0;
+	if (raw_irqs_disabled()) {
+		_disabled++;
+	} else {
+		_enabled++;
+		printk(KERN_CRIT "USB_HCD_IRQ interrupts disabled %d enabled %d\n",
+		       _disabled, _enabled);
+	}
+#endif
+
 	if (unlikely(start == HC_STATE_HALT ||
 	    !test_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags)))
 		return IRQ_NONE;

[-- Attachment #3: proc-interrupts.txt --]
[-- Type: text/plain, Size: 914 bytes --]

           CPU0       
  0:      31904    XT-PIC-XT        timer
  1:        112    XT-PIC-XT        i8042
  2:          0    XT-PIC-XT        cascade
  5:          1    XT-PIC-XT        firewire_ohci, VIA8233, VIA82XX-MODEM
  6:          1    XT-PIC-XT      
  7:          0    XT-PIC-XT        parport0
  9:         52    XT-PIC-XT        acpi
 10:         21    XT-PIC-XT        uhci_hcd:usb2
 11:         36    XT-PIC-XT        yenta, ehci_hcd:usb1, uhci_hcd:usb3
 12:        120    XT-PIC-XT        i8042
 14:       1959    XT-PIC-XT        pata_via
 15:         39    XT-PIC-XT        pata_via
NMI:          0   Non-maskable interrupts
LOC:          0   Local timer interrupts
RES:          0   Rescheduling interrupts
CAL:          0   function call interrupts
TLB:          0   TLB shootdowns
TRM:          0   Thermal event interrupts
SPU:          0   Spurious interrupts
ERR:          0
MIS:          0