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Message-ID: <42295bfc-136d-ebac-c44e-6bf46b0757f9@arm.com>
Date: Fri, 26 Aug 2022 12:35:11 +0200
From: Pierre Gondois <pierre.gondois@....com>
To: Song Chen <chensong_2000@....cn>, linux-kernel@...r.kernel.org,
linux-rt-users@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH] irqchip/gic-v3-its: Remove cpumask_var_t allocation
Hello Song,
On 8/26/22 03:17, Song Chen wrote:
> hi,
>
> 在 2022/8/25 23:23, Pierre Gondois 写道:
>> In KvmTool, on a ThunderX2, when running a preemp_rt kernel based on
>> v5.19-rc3-rt4, the following happens:
>> [ 4.070739] [ BUG: Invalid wait context ]
>> [ 4.070740] 5.19.0-rc3-rt4-00001-g1a6597c0bdcf #153 Not tainted
>> [ 4.070742] -----------------------------
>> [ 4.070743] swapper/0/1 is trying to lock:
>> [ 4.070744] ffff0000ab7405d8 ((&c->lock)){+.+.}-{3:3}, at: ___slab_alloc (mm/slub.c:2954)
>> [ 4.070757] other info that might help us debug this:
>> [ 4.070758] context-{5:5}
>> [ 4.070759] 5 locks held by swapper/0/1:
>> [ 4.070760] #0: ffff0000811491e0 (&dev->mutex){....}-{4:4}, at: __device_driver_lock (drivers/base/dd.c:1055)
>> [ 4.070769] #1: ffff0000846c5670 (&desc->request_mutex){+.+.}-{4:4}, at: __setup_irq (kernel/irq/internals.h:147)
>> [ 4.070778] #2: ffff0000846c54c8 (&irq_desc_lock_class){....}-{2:2}, at: __setup_irq (kernel/irq/manage.c:1612)
>> [ 4.070784] #3: ffff80000b23ea78 (mask_lock){....}-{2:2}, at: irq_setup_affinity (./include/linux/irq.h:381)
>> [ 4.070791] #4: ffff80000b23ea38 (tmp_mask_lock){....}-{2:2}, at: irq_do_set_affinity (./include/linux/irq.h:381)
>> [ 4.070797] stack backtrace:
>> [ 4.070801] CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.19.0-rc3-rt4-00001-g1a6597c0bdcf #153
>> [ 4.070805] Call trace:
>> [ 4.070806] dump_backtrace (arch/arm64/kernel/stacktrace.c:200)
>> [ 4.070811] show_stack (arch/arm64/kernel/stacktrace.c:207)
>> [ 4.070813] dump_stack_lvl (lib/dump_stack.c:107)
>> [ 4.070818] dump_stack (lib/dump_stack.c:114)
>> [ 4.070820] __lock_acquire (kernel/locking/lockdep.c:4707)
>> [ 4.070823] lock_acquire (kernel/locking/lockdep.c:466)
>> [ 4.070825] rt_spin_lock (./arch/arm64/include/asm/current.h:19 (discriminator 4))
>> [ 4.070830] ___slab_alloc (mm/slub.c:2954)
>> [ 4.070832] __slab_alloc.isra.0 (mm/slub.c:3116)
>> [ 4.070835] __kmalloc_node (mm/slub.c:3207)
>> [ 4.070837] alloc_cpumask_var_node (lib/cpumask.c:115)
>> [ 4.070843] alloc_cpumask_var (lib/cpumask.c:147)
>> [ 4.070846] its_select_cpu (drivers/irqchip/irq-gic-v3-its.c:1580)
>> [ 4.070850] its_set_affinity (drivers/irqchip/irq-gic-v3-its.c:1659)
>> [ 4.070853] msi_domain_set_affinity (kernel/irq/msi.c:501)
>> [ 4.070857] irq_do_set_affinity (kernel/irq/manage.c:276)
>> [ 4.070860] irq_setup_affinity (kernel/irq/manage.c:633)
>> [ 4.070863] irq_startup (kernel/irq/chip.c:280)
>> [ 4.070865] __setup_irq (kernel/irq/manage.c:1777)
>> [ 4.070869] request_threaded_irq (kernel/irq/manage.c:2206)
>> [ 4.070872] vp_find_vqs_msix (./include/linux/interrupt.h:168)
>> [ 4.070876] vp_find_vqs (drivers/virtio/virtio_pci_common.c:400)
>> [ 4.070878] vp_modern_find_vqs (drivers/virtio/virtio_pci_modern.c:259)
>> [ 4.070880] init_vq (./include/linux/virtio_config.h:213)
>> [ 4.070885] virtblk_probe (drivers/block/virtio_blk.c:936)
>> [ 4.070887] virtio_dev_probe (drivers/virtio/virtio.c:303)
>> [ 4.070892] really_probe (drivers/base/dd.c:555)
>> [ 4.070895] __driver_probe_device (drivers/base/dd.c:764)
>> [ 4.070897] driver_probe_device (drivers/base/dd.c:794)
>> [ 4.070899] __driver_attach (drivers/base/dd.c:1164)
>> [ 4.070901] bus_for_each_dev (drivers/base/bus.c:301)
>> [ 4.070904] driver_attach (drivers/base/dd.c:1181)
>> [ 4.070906] bus_add_driver (drivers/base/bus.c:618)
>> [ 4.070908] driver_register (drivers/base/driver.c:240)
>> [ 4.070910] register_virtio_driver (drivers/virtio/virtio.c:356 (discriminator 4))
>> [ 4.070913] virtio_blk_init (drivers/block/virtio_blk.c:1218)
>> [ 4.070918] do_one_initcall (init/main.c:1295)
>> [ 4.070921] kernel_init_freeable (init/main.c:1367)
>> [ 4.070924] kernel_init (init/main.c:1503)
>> [ 4.070927] ret_from_fork (arch/arm64/kernel/entry.S:868)
>>
>> commit cba4235e6031e ("genirq: Remove mask argument from
>> setup_affinity()")
>> and
>> commit 11ea68f553e24 ("genirq, sched/isolation: Isolate from handling
>> managed interrupts")
>> overcome this issue by defining a static struct cpumask and protecting
>> it by a raw spinlock. The code in these commits is executed with IRQs
>> disabled.
>> its_select_cpu() can be executed with IRQs enabled or disabled. Thus
>> disabling IRQs is necesserary to avoid deadlocking.
>>
>> This patch:
>> - makes tmpmask a 'static struct cpumask'. This prevents storing it on
>> the stack and having to dynamically allocate it
>> - protects tmpmask with a raw spinlock
>> - disables IRQs around the spinlock for the case its_select_cpu() is
>> called with IRQs enabled
>>
>> Signed-off-by: Pierre Gondois <pierre.gondois@....com>
>> ---
>> drivers/irqchip/irq-gic-v3-its.c | 34 +++++++++++++++++---------------
>> 1 file changed, 18 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 5ff09de6c48f..3cf89e59b036 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -1574,14 +1574,15 @@ static int its_select_cpu(struct irq_data *d,
>> const struct cpumask *aff_mask)
>> {
>> struct its_device *its_dev = irq_data_get_irq_chip_data(d);
>> - cpumask_var_t tmpmask;
>> + static DEFINE_RAW_SPINLOCK(tmpmask_lock);
>> + static struct cpumask tmpmask;
>> + unsigned long flags;
>> int cpu, node;
>> -
>> - if (!alloc_cpumask_var(&tmpmask, GFP_ATOMIC))
>> - return -ENOMEM;
>> -
>> node = its_dev->its->numa_node;
>>
>> + local_irq_save(flags);
>> + raw_spin_lock(&tmpmask_lock);
>> +
>
> why not call raw_spin_lock_irqsave and raw_spin_unlock_irqrestore?
Yes indeed, raw_spin_unlock_irqrestore() would fit perfectly,
this is a mistake.
Thanks for the review,
Pierre
>
> Song
>
>> if (!irqd_affinity_is_managed(d)) {
>> /* First try the NUMA node */
>> if (node != NUMA_NO_NODE) {
>> @@ -1589,8 +1590,8 @@ static int its_select_cpu(struct irq_data *d,
>> * Try the intersection of the affinity mask and the
>> * node mask (and the online mask, just to be safe).
>> */
>> - cpumask_and(tmpmask, cpumask_of_node(node), aff_mask);
>> - cpumask_and(tmpmask, tmpmask, cpu_online_mask);
>> + cpumask_and(&tmpmask, cpumask_of_node(node), aff_mask);
>> + cpumask_and(&tmpmask, &tmpmask, cpu_online_mask);
>>
>> /*
>> * Ideally, we would check if the mask is empty, and
>> @@ -1604,7 +1605,7 @@ static int its_select_cpu(struct irq_data *d,
>> * Instead, just fallback on the online mask. This
>> * diverges from Thomas' suggestion above.
>> */
>> - cpu = cpumask_pick_least_loaded(d, tmpmask);
>> + cpu = cpumask_pick_least_loaded(d, &tmpmask);
>> if (cpu < nr_cpu_ids)
>> goto out;
>>
>> @@ -1616,25 +1617,26 @@ static int its_select_cpu(struct irq_data *d,
>> }
>>
>> /* Try the intersection of the affinity and online masks */
>> - cpumask_and(tmpmask, aff_mask, cpu_online_mask);
>> + cpumask_and(&tmpmask, aff_mask, cpu_online_mask);
>>
>> /* If that doesn't fly, the online mask is the last resort */
>> - if (cpumask_empty(tmpmask))
>> - cpumask_copy(tmpmask, cpu_online_mask);
>> + if (cpumask_empty(&tmpmask))
>> + cpumask_copy(&tmpmask, cpu_online_mask);
>>
>> - cpu = cpumask_pick_least_loaded(d, tmpmask);
>> + cpu = cpumask_pick_least_loaded(d, &tmpmask);
>> } else {
>> - cpumask_copy(tmpmask, aff_mask);
>> + cpumask_copy(&tmpmask, aff_mask);
>>
>> /* If we cannot cross sockets, limit the search to that node */
>> if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144) &&
>> node != NUMA_NO_NODE)
>> - cpumask_and(tmpmask, tmpmask, cpumask_of_node(node));
>> + cpumask_and(&tmpmask, &tmpmask, cpumask_of_node(node));
>>
>> - cpu = cpumask_pick_least_loaded(d, tmpmask);
>> + cpu = cpumask_pick_least_loaded(d, &tmpmask);
>> }
>> out:
>> - free_cpumask_var(tmpmask);
>> + raw_spin_unlock(&tmpmask_lock);
>> + local_irq_restore(flags);
>>
>> pr_debug("IRQ%d -> %*pbl CPU%d\n", d->irq, cpumask_pr_args(aff_mask), cpu);
>> return cpu;
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