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Message #78963
[Bug 1359514] Re: pci-xgene-msi: fixed deadlock in irq_set_affinity
** Branch linked: lp:ubuntu/precise-proposed/linux-lts-trusty
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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:
In Progress
Status in “linux” source package in Trusty:
Fix Committed
Status in “linux” source package in Utopic:
In Progress
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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References