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My >>> kernel was linux-next 20260128. I set CONFIG_PREEMPT_RT=y and >>> CONFIG_PROVE_LOCKING=y, but did not add either of your two patches >>> (neither the storvsc driver patch nor the x86 VMBus interrupt handling patch). >>> The VM comes up and runs, but with this warning during boot: >>> >>> [ 3.075604] hv_utils: Registering HyperV Utility Driver >>> [ 3.075636] hv_vmbus: registering driver hv_utils >>> [ 3.085920] ============================= >>> [ 3.088128] hv_vmbus: registering driver hv_netvsc >>> [ 3.091180] [ BUG: Invalid wait context ] >>> [ 3.093544] 6.19.0-rc7-next-20260128+ #3 Tainted: G E >>> [ 3.097582] ----------------------------- >>> [ 3.099899] systemd-udevd/284 is trying to lock: >>> [ 3.102568] ffff000100e24490 (&channel->sched_lock){....}-{3:3}, at: vmbus_chan_sched+0x128/0x3b8 [hv_vmbus] >>> [ 3.108208] other info that might help us debug this: >>> [ 3.111454] context-{2:2} >>> [ 3.112987] 1 lock held by systemd-udevd/284: >>> [ 3.115626] #0: ffffd5cfc20bcc80 (rcu_read_lock){....}-{1:3}, at: vmbus_chan_sched+0xcc/0x3b8 [hv_vmbus] >>> [ 3.121224] stack backtrace: >>> [ 3.122897] CPU: 0 UID: 0 PID: 284 Comm: systemd-udevd Tainted: G E 6.19.0-rc7-next-20260128+ #3 PREEMPT_RT >>> [ 3.129631] Tainted: [E]=UNSIGNED_MODULE >>> [ 3.131946] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 06/10/2025 >>> [ 3.138553] Call trace: >>> [ 3.140015] show_stack+0x20/0x38 (C) >>> [ 3.142137] dump_stack_lvl+0x9c/0x158 >>> [ 3.144340] dump_stack+0x18/0x28 >>> [ 3.146290] __lock_acquire+0x488/0x1e20 >>> [ 3.148569] lock_acquire+0x11c/0x388 >>> [ 3.150703] rt_spin_lock+0x54/0x230 >>> [ 3.152785] vmbus_chan_sched+0x128/0x3b8 [hv_vmbus] >>> [ 3.155611] vmbus_isr+0x34/0x80 [hv_vmbus] >>> [ 3.158093] vmbus_percpu_isr+0x18/0x30 [hv_vmbus] >>> [ 3.160848] handle_percpu_devid_irq+0xdc/0x348 >>> [ 3.163495] handle_irq_desc+0x48/0x68 >>> [ 3.165851] generic_handle_domain_irq+0x20/0x38 >>> [ 3.168664] gic_handle_irq+0x1dc/0x430 >>> [ 3.170868] call_on_irq_stack+0x30/0x70 >>> [ 3.173161] do_interrupt_handler+0x88/0xa0 >>> [ 3.175724] el1_interrupt+0x4c/0xb0 >>> [ 3.177855] el1h_64_irq_handler+0x18/0x28 >>> [ 3.180332] el1h_64_irq+0x84/0x88 >>> [ 3.182378] _raw_spin_unlock_irqrestore+0x4c/0xb0 (P) >>> [ 3.185493] rt_mutex_slowunlock+0x404/0x440 >>> [ 3.187951] rt_spin_unlock+0xb8/0x178 >>> [ 3.190394] kmem_cache_alloc_noprof+0xf0/0x4f8 >>> [ 3.193100] alloc_empty_file+0x64/0x148 >>> [ 3.195461] path_openat+0x58/0xaa0 >>> [ 3.197658] do_file_open+0xa0/0x140 >>> [ 3.199752] do_sys_openat2+0x190/0x278 >>> [ 3.202124] do_sys_open+0x60/0xb8 >>> [ 3.204047] __arm64_sys_openat+0x2c/0x48 >>> [ 3.206433] invoke_syscall+0x6c/0xf8 >>> [ 3.208519] el0_svc_common.constprop.0+0x48/0xf0 >>> [ 3.211050] do_el0_svc+0x24/0x38 >>> [ 3.212990] el0_svc+0x164/0x3c8 >>> [ 3.214842] el0t_64_sync_handler+0xd0/0xe8 >>> [ 3.217251] el0t_64_sync+0x1b0/0x1b8 >>> [ 3.219450] hv_utils: Heartbeat IC version 3.0 >>> [ 3.219471] hv_utils: Shutdown IC version 3.2 >>> [ 3.219844] hv_utils: TimeSync IC version 4.0 >> >> That matches with my expectation that the same problem exists on arm64. >> The patch from Jan addresses that issue for x86 (only, so far) as we do >> not have a working test environment for arm64 yet. > > OK. I had understood Jan's earlier comments to mean that the VMBus > interrupt problem was implicitly solved on arm64 because of VMBus using > a standard Linux IRQ on arm64. But evidently that's not the case. So my > earlier comment stands: The code changes should go into the architecture > independent portion of the VMBus driver, and not under arch/x86. I > can probably work with you to test on arm64 if need be. > I can move the code, sure, but I still haven't understood what invalidates my assumptions (beside what you observed). vmbus_drv calls request_percpu_irq, and that is - as far as I can see - not injecting IRQF_NO_THREAD. Any explanations welcome. Reproduction is still not possible for me. I was playing a bit with qemu in the hope to make it provide its minimal vmbus support (for ballooning), but that was not yet successful on arm64. Jan -- Siemens AG, Foundational Technologies Linux Expert Center