From: Jan Kiszka <[email protected]>
Resolves the following lockdep report when booting PREEMPT_RT on Hyper-V
with related guest support enabled:
[ 1.127941] hv_vmbus: registering driver hyperv_drm
[ 1.132518] =============================
[ 1.132519] [ BUG: Invalid wait context ]
[ 1.132521] 6.19.0-rc8+ #9 Not tainted
[ 1.132524] -----------------------------
[ 1.132525] swapper/0/0 is trying to lock:
[ 1.132526] ffff8b9381bb3c90 (&channel->sched_lock){....}-{3:3}, at:
vmbus_chan_sched+0xc4/0x2b0
[ 1.132543] other info that might help us debug this:
[ 1.132544] context-{2:2}
[ 1.132545] 1 lock held by swapper/0/0:
[ 1.132547] #0: ffffffffa010c4c0 (rcu_read_lock){....}-{1:3}, at:
vmbus_chan_sched+0x31/0x2b0
[ 1.132557] stack backtrace:
[ 1.132560] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.19.0-rc8+ #9
PREEMPT_{RT,(lazy)}
[ 1.132565] Hardware name: Microsoft Corporation Virtual Machine/Virtual
Machine, BIOS Hyper-V UEFI Release v4.1 09/25/2025
[ 1.132567] Call Trace:
[ 1.132570] <IRQ>
[ 1.132573] dump_stack_lvl+0x6e/0xa0
[ 1.132581] __lock_acquire+0xee0/0x21b0
[ 1.132592] lock_acquire+0xd5/0x2d0
[ 1.132598] ? vmbus_chan_sched+0xc4/0x2b0
[ 1.132606] ? lock_acquire+0xd5/0x2d0
[ 1.132613] ? vmbus_chan_sched+0x31/0x2b0
[ 1.132619] rt_spin_lock+0x3f/0x1f0
[ 1.132623] ? vmbus_chan_sched+0xc4/0x2b0
[ 1.132629] ? vmbus_chan_sched+0x31/0x2b0
[ 1.132634] vmbus_chan_sched+0xc4/0x2b0
[ 1.132641] vmbus_isr+0x2c/0x150
[ 1.132648] __sysvec_hyperv_callback+0x5f/0xa0
[ 1.132654] sysvec_hyperv_callback+0x88/0xb0
[ 1.132658] </IRQ>
[ 1.132659] <TASK>
[ 1.132660] asm_sysvec_hyperv_callback+0x1a/0x20
As code paths that handle vmbus IRQs use sleepy locks under PREEMPT_RT,
the vmbus_isr execution needs to be moved into thread context. Open-
coding this allows to skip the IPI that irq_work would additionally
bring and which we do not need, being an IRQ, never an NMI.
This affects both x86 and arm64, therefore hook into the common driver
logic.
Signed-off-by: Jan Kiszka <[email protected]>
---
Changes in v3:
- move logic to generic vmbus driver, targeting arm64 as well
- annotate non-RT path with lockdep_hardirq_threaded
- only teardown if setup ran
Changes in v2:
- reorder vmbus_irq_pending clearing to fix a race condition
drivers/hv/vmbus_drv.c | 66 +++++++++++++++++++++++++++++++++++++++++-
1 file changed, 65 insertions(+), 1 deletion(-)
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 6785ad63a9cb..749a2e68af05 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -25,6 +25,7 @@
#include <linux/cpu.h>
#include <linux/sched/isolation.h>
#include <linux/sched/task_stack.h>
+#include <linux/smpboot.h>
#include <linux/delay.h>
#include <linux/panic_notifier.h>
@@ -1350,7 +1351,7 @@ static void vmbus_message_sched(struct hv_per_cpu_context
*hv_cpu, void *message
}
}
-void vmbus_isr(void)
+static void __vmbus_isr(void)
{
struct hv_per_cpu_context *hv_cpu
= this_cpu_ptr(hv_context.cpu_context);
@@ -1363,6 +1364,53 @@ void vmbus_isr(void)
add_interrupt_randomness(vmbus_interrupt);
}
+
+static DEFINE_PER_CPU(bool, vmbus_irq_pending);
+static DEFINE_PER_CPU(struct task_struct *, vmbus_irqd);
+
+static void vmbus_irqd_wake(void)
+{
+ struct task_struct *tsk = __this_cpu_read(vmbus_irqd);
+
+ __this_cpu_write(vmbus_irq_pending, true);
+ wake_up_process(tsk);
+}
+
+static void vmbus_irqd_setup(unsigned int cpu)
+{
+ sched_set_fifo(current);
+}
+
+static int vmbus_irqd_should_run(unsigned int cpu)
+{
+ return __this_cpu_read(vmbus_irq_pending);
+}
+
+static void run_vmbus_irqd(unsigned int cpu)
+{
+ __this_cpu_write(vmbus_irq_pending, false);
+ __vmbus_isr();
+}
+
+static bool vmbus_irq_initialized;
+
+static struct smp_hotplug_thread vmbus_irq_threads = {
+ .store = &vmbus_irqd,
+ .setup = vmbus_irqd_setup,
+ .thread_should_run = vmbus_irqd_should_run,
+ .thread_fn = run_vmbus_irqd,
+ .thread_comm = "vmbus_irq/%u",
+};
+
+void vmbus_isr(void)
+{
+ if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+ vmbus_irqd_wake();
+ } else {
+ lockdep_hardirq_threaded();
+ __vmbus_isr();
+ }
+}
EXPORT_SYMBOL_FOR_MODULES(vmbus_isr, "mshv_vtl");
static irqreturn_t vmbus_percpu_isr(int irq, void *dev_id)
@@ -1462,6 +1510,13 @@ static int vmbus_bus_init(void)
* the VMbus interrupt handler.
*/
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && !vmbus_irq_initialized) {
+ ret = smpboot_register_percpu_thread(&vmbus_irq_threads);
+ if (ret)
+ goto err_kthread;
+ vmbus_irq_initialized = true;
+ }
+
if (vmbus_irq == -1) {
hv_setup_vmbus_handler(vmbus_isr);
} else {
@@ -1507,6 +1562,11 @@ static int vmbus_bus_init(void)
free_percpu(vmbus_evt);
}
err_setup:
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && vmbus_irq_initialized) {
+ smpboot_unregister_percpu_thread(&vmbus_irq_threads);
+ vmbus_irq_initialized = false;
+ }
+err_kthread:
bus_unregister(&hv_bus);
return ret;
}
@@ -2976,6 +3036,10 @@ static void __exit vmbus_exit(void)
free_percpu_irq(vmbus_irq, vmbus_evt);
free_percpu(vmbus_evt);
}
+ if (IS_ENABLED(CONFIG_PREEMPT_RT) && vmbus_irq_initialized) {
+ smpboot_unregister_percpu_thread(&vmbus_irq_threads);
+ vmbus_irq_initialized = false;
+ }
for_each_online_cpu(cpu) {
struct hv_per_cpu_context *hv_cpu
= per_cpu_ptr(hv_context.cpu_context, cpu);
--
2.47.3
