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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

** Changed in: linux (Ubuntu)
       Status: Confirmed => Triaged

** Tags added: patch

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https://bugs.launchpad.net/bugs/1359514

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

Status in “linux” package in Ubuntu:
  Triaged

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.

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