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[Craig Magina <1359514@xxxxxxxxxxxxxxxxxx>]

** Patch removed: "0001-UBUNTU-SAUCE-no-up-pci-xgene-msi-fixed-deadlock-in-i.patch"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1359514/+attachment/4188555/+files/0001-UBUNTU-SAUCE-no-up-pci-xgene-msi-fixed-deadlock-in-i.patch

** Patch added: "0001-UBUNTU-SAUCE-no-up-pci-xgene-msi-fixed-deadlock-in-i.patch"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1359514/+attachment/4188597/+files/0001-UBUNTU-SAUCE-no-up-pci-xgene-msi-fixed-deadlock-in-i.patch

** Description changed:

+ [IMPACT]
  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.
+ 
+     + 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.
+ 
+ [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.

-- 
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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:
  [IMPACT]
  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.

  [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.

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