Hi Tony, * Alex Chiang <achiang@xxxxxx>: > This reverts commit e7b140365b86aaf94374214c6f4e6decbee2eb0a. > > Commit e7b14036 removes the targetted disabled CPU from the > cpu_online_map after calls to migrate_platform_irqs and fixup_irqs. I'm currently testing the patch below as a v3. > Paul McKenney states that the reasoning behind the patch was to > prevent irq handlers from running on CPUs marked offline because: > > RCU happily ignores CPUs that don't have their bits set in > cpu_online_map, so if there are RCU read-side critical sections > in the irq handlers being run, RCU will ignore them. If the > other CPUs were running, they might sequence through the RCU > state machine, which could result in data structures being > yanked out from under those irq handlers, which in turn could > result in oopses or worse. > > Unfortunately, both ia64 functions above look at cpu_online_map to find > a new CPU to migrate interrupts onto. This means we can potentially > migrate an interrupt off ourself back to... ourself. Uh oh. v3 uses cpu_active_mask to find an interrupt migration target. This should fix both the oops we were seeing as well as avoid the issues with RCU that Paul mentions above. I also think that this fix is simpler for us to think through rather than making Paul think through the implications of changing RCU to use cpu_active_mask. :) So far, it's survived ~45 minutes on my simple test bed (without any patches, it usually crashes in < 15 minutes). I'm about to start a longer run on our complex test system that runs under heavy load. Hopefully I'll have some results for tomorrow, in which case I'll send a proper patch. Thanks. /ac diff --git a/arch/ia64/kernel/irq.c b/arch/ia64/kernel/irq.c index a58f64c..9eaab3c 100644 --- a/arch/ia64/kernel/irq.c +++ b/arch/ia64/kernel/irq.c @@ -155,7 +155,7 @@ static void migrate_irqs(void) */ vectors_in_migration[irq] = irq; - new_cpu = cpumask_any(cpu_online_mask); + new_cpu = cpumask_any(cpu_active_mask); /* * Al three are essential, currently WARN_ON.. maybe panic? diff --git a/arch/ia64/kernel/smpboot.c b/arch/ia64/kernel/smpboot.c index 1146399..4e8765d 100644 --- a/arch/ia64/kernel/smpboot.c +++ b/arch/ia64/kernel/smpboot.c @@ -694,7 +694,7 @@ int migrate_platform_irqs(unsigned int cpu) /* * Now re-target the CPEI to a different processor */ - new_cpei_cpu = any_online_cpu(cpu_online_map); + new_cpei_cpu = cpumask_any(cpu_active_mask); mask = cpumask_of(new_cpei_cpu); set_cpei_target_cpu(new_cpei_cpu); desc = irq_desc + ia64_cpe_irq; -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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