From: Neil Horman nhorman@tuxdriver.com
[ Upstream commit 743dac494d61d991967ebcfab92e4f80dc7583b3 ]
On x86, CPUs are limited in the number of interrupts they can have affined to them as they only support 256 interrupt vectors per CPU. 32 vectors are reserved for the CPU and the kernel reserves another 22 for internal purposes. That leaves 202 vectors for assignement to devices.
When an interrupt is set up or the affinity is changed by the kernel or the administrator, the vector assignment code attempts to honor the requested affinity mask. If the vector space on the CPUs in that affinity mask is exhausted the code falls back to a wider set of CPUs and assigns a vector on a CPU outside of the requested affinity mask silently.
While the effective affinity is reflected in the corresponding /proc/irq/$N/effective_affinity* files the silent breakage of the requested affinity can lead to unexpected behaviour for administrators.
Add a pr_warn() when this happens so that adminstrators get at least informed about it in the syslog.
[ tglx: Massaged changelog and made the pr_warn() more informative ]
Reported-by: djuran@redhat.com Signed-off-by: Neil Horman nhorman@tuxdriver.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: djuran@redhat.com Link: https://lkml.kernel.org/r/20190822143421.9535-1-nhorman@tuxdriver.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/apic/vector.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c index 10e1d17aa0608..c352ca2e1456f 100644 --- a/arch/x86/kernel/apic/vector.c +++ b/arch/x86/kernel/apic/vector.c @@ -400,6 +400,17 @@ static int activate_reserved(struct irq_data *irqd) if (!irqd_can_reserve(irqd)) apicd->can_reserve = false; } + + /* + * Check to ensure that the effective affinity mask is a subset + * the user supplied affinity mask, and warn the user if it is not + */ + if (!cpumask_subset(irq_data_get_effective_affinity_mask(irqd), + irq_data_get_affinity_mask(irqd))) { + pr_warn("irq %u: Affinity broken due to vector space exhaustion.\n", + irqd->irq); + } + return ret; }