kernel-packages team mailing list archive

[Craig Magina <1359514@xxxxxxxxxxxxxxxxxx>]

[IMPACT]
The CPU x doesn't have a chance to exit the xgene_msi_cascade function to unlock desc->lock before Linux scheduce and call xgene_msi_set_affinity (irqbalance is caller) in the same CPU x. In irq_set_affinity, call raw_spin_lock_irqsave(&desc->lock, flags) which cause deadlock to CPU x because it disables preempt.

Use chained_irq_enter and exit as the standard way to cascade interrupt
functions.

[TEST CASE]
Turn off irqbalance
Run a single tcp stream
Randomly change the affinity of the receiving ring:

@ ethtool -S $INTF | grep rx[0-9].*_pac @ - to detect the rx ring
@ grep $INTF /proc/interrupts@ - to find it's interrupt
@ printf "%x" $(( 2 ** $((RANDOM % 8)) )) > /proc/irq/$IRQ/smp_affinity @ - to change the affinity

[Regression Potential]
Fix specific to the xgene pci msi code.

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1359514

Title:
  pci-xgene-msi: fixed deadlock in irq_set_affinity

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  Issue:  CPU affinity is changed while irqbalance is running.
      
      + Problem explanation:
      
        - Old code
      
          + Call xgene_msi_cascade function (CPU x)
      
          + raw_spin_lock(&desc->lock);  (CPU x)
      
          + Goto generic_handle_irq (CPU x)
      
          + The CPU x doesn't have a chance to exit the xgene_msi_cascade function to unlock desc->lock before Linux scheduce and call xgene_msi_set_affinity (irqbalance is caller) in the same CPU x
      
          + In irq_set_affinity, call raw_spin_lock_irqsave(&desc->lock, flags) which cause deadlock to CPU x because it disables preempt
      
        - New code
      
          + Use chained_irq_enter and exit as the standard way to cascade interrupt functions.

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1359514/+subscriptions