It was pointed out by Nitesh that the original work I did in 2014 to automatically set the interrupt affinity when requesting a mask is no longer necessary. The kernel has moved on and no longer has the original problem, BUT the original patch introduced a subtle bug when booting a system with reserved or excluded CPUs. Drivers calling this function with a mask value that included a CPU that was currently or in the future unavailable would generally not update the hint. I'm sure there are a million ways to solve this, but the simplest one is to just remove a little code that tries to force the affinity, as Nitesh has shown it fixes the bug and doesn't seem to introduce immediate side effects. While I'm here, introduce a kernel-doc for the hint function. Ref: https://lore.kernel.org/lkml/CAFki+L=_dd+JgAR12_eBPX0kZO2_6=1dGdgkwHE=u=K6chMeLQ@xxxxxxxxxxxxxx/ Cc: netdev@xxxxxxxxxxxxxxx Fixes: 4fe7ffb7e17c ("genirq: Fix null pointer reference in irq_set_affinity_hint()") Fixes: e2e64a932556 ("genirq: Set initial affinity in irq_set_affinity_hint()") Reported-by: Nitesh Lal <nilal@xxxxxxxxxx> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@xxxxxxxxx> --- !!! NOTE: Compile tested only, would appreciate feedback --- kernel/irq/manage.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index e976c4927b25..a31df64662d5 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -456,6 +456,16 @@ int __irq_set_affinity(unsigned int irq, const struct cpumask *mask, bool force) return ret; } +/** + * irq_set_affinity_hint - set the hint for an irq + * @irq: Interrupt for which to set the hint + * @m: Mask to indicate which CPUs to suggest for the interrupt, use + * NULL here to indicate to clear the value. + * + * Use this function to recommend which CPU should handle the + * interrupt to any userspace that uses /proc/irq/nn/smp_affinity_hint + * in order to align interrupts. Pass NULL as the mask to clear the hint. + */ int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m) { unsigned long flags; @@ -465,9 +475,6 @@ int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m) return -EINVAL; desc->affinity_hint = m; irq_put_desc_unlock(desc, flags); - /* set the initial affinity to prevent every interrupt being on CPU0 */ - if (m) - __irq_set_affinity(irq, m, false); return 0; } EXPORT_SYMBOL_GPL(irq_set_affinity_hint); base-commit: 765822e1569a37aab5e69736c52d4ad4a289eba6 -- 2.30.2
