--- /dev/null
+From f8e6343b7a89c7c649db5a9e309ba7aa20401813 Mon Sep 17 00:00:00 2001
+From: Jan Kiszka <jan.kiszka@siemens.com>
+Date: Mon, 16 Feb 2026 17:24:56 +0100
+Subject: Drivers: hv: vmbus: Use kthread for vmbus interrupts on PREEMPT_RT
+
+From: Jan Kiszka <jan.kiszka@siemens.com>
+
+commit f8e6343b7a89c7c649db5a9e309ba7aa20401813 upstream.
+
+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 <jan.kiszka@siemens.com>
+Reviewed-by: Florian Bezdeka <florian.bezdeka@siemens.com>
+Tested-by: Florian Bezdeka <florian.bezdeka@siemens.com>
+Reviewed-by: Michael Kelley <mhklinux@outlook.com>
+Tested-by: Michael Kelley <mhklinux@outlook.com>
+Signed-off-by: Wei Liu <wei.liu@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/hv/vmbus_drv.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++-
+ 1 file changed, 65 insertions(+), 1 deletion(-)
+
+--- 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>
+@@ -1276,7 +1277,7 @@ sched_unlock_rcu:
+ }
+ }
+
+-static void vmbus_isr(void)
++static void __vmbus_isr(void)
+ {
+ struct hv_per_cpu_context *hv_cpu
+ = this_cpu_ptr(hv_context.cpu_context);
+@@ -1300,6 +1301,53 @@ static 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",
++};
++
++static void vmbus_isr(void)
++{
++ if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
++ vmbus_irqd_wake();
++ } else {
++ lockdep_hardirq_threaded();
++ __vmbus_isr();
++ }
++}
++
+ static irqreturn_t vmbus_percpu_isr(int irq, void *dev_id)
+ {
+ vmbus_isr();
+@@ -1345,6 +1393,13 @@ 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 {
+@@ -1419,6 +1474,11 @@ err_alloc:
+ 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;
+ }
+@@ -2818,6 +2878,10 @@ 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);
projects / thirdparty / kernel / stable-queue.git / commitdiff
