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vduse: avoid infinite loop when no affinity CPU is online

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If all CPUs in vq->irq_affinity are offline, cpumask_next() walks to the
end of the mask, and the loop then resets the cursor to IRQ_UNBOUND and
restarts the scan. When VDUSE_VQ_INJECT_IRQ is issued, the intersection of
vq->irq_affinity and cpu_online_mask is empty, so the caller busy-loops in
kernel context on its current CPU (e.g. CPU2).

Replace the while loop in vduse_vq_update_effective_cpu() with
cpumask_next_and_wrap() to find the intersection of vq->irq_affinity and
cpu_online_mask in a single wrapped scan. If the intersection is empty, set
curr_cpu to IRQ_UNBOUND and let the existing unbound workqueue handle
injection, avoiding repeated rescans when all CPUs in the affinity are
offline. Use cpus_read_lock()/cpus_read_unlock() to keep the selected CPU
online.

Fixes: 28f6288eb6 ("vduse: Support set_vq_affinity callback")
Signed-off-by: Jia Jia <physicalmtea@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20260919083933.104437-1-physicalmtea@gmail.com>
This commit is contained in:
Jia Jia 2026-09-19 16:39:33 +08:00 committed by Michael S. Tsirkin
parent 434d2bc41b
commit cf0a5805d4
1 changed files with 7 additions and 8 deletions
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15
drivers/vdpa/vdpa_user/vduse_dev.c
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@ -15,6 +15,7 @@
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/cpu.h>
#include <linux/eventfd.h>
#include <linux/slab.h>
#include <linux/wait.h>
@ -1430,14 +1431,10 @@ static void vduse_vq_update_effective_cpu(struct vduse_virtqueue *vq)
{
int curr_cpu = vq->irq_effective_cpu;
while (true) {
curr_cpu = cpumask_next(curr_cpu, &vq->irq_affinity);
if (cpu_online(curr_cpu))
break;
if (curr_cpu >= nr_cpu_ids)
curr_cpu = IRQ_UNBOUND;
}
curr_cpu = cpumask_next_and_wrap(curr_cpu, &vq->irq_affinity,
cpu_online_mask);
if (curr_cpu >= nr_cpu_ids)
curr_cpu = IRQ_UNBOUND;
vq->irq_effective_cpu = curr_cpu;
}
@ -1672,10 +1669,12 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
ret = 0;
index = array_index_nospec(index, dev->vq_num);
if (!vduse_vq_signal_irqfd(dev->vqs[index])) {
cpus_read_lock();
vduse_vq_update_effective_cpu(dev->vqs[index]);
ret = vduse_dev_queue_irq_work(dev,
&dev->vqs[index]->inject,
dev->vqs[index]->irq_effective_cpu);
cpus_read_unlock();
}
break;
}