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List: linux-rt-users
Subject: Re: [PATCH] irqchip/gic-v3-its: Remove cpumask_var_t allocation
From: Pierre Gondois <pierre.gondois () arm ! com>
Date: 2022-08-26 10:35:11
Message-ID: 42295bfc-136d-ebac-c44e-6bf46b0757f9 () arm ! com
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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@arm.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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