Re: [PATCH v3] drivers: hv: vmbus: Use kthread for vmbus interrupts on PREEMPT_RT

[Wei Liu <wei.liu@kernel.org>]

On Mon, Feb 16, 2026 at 05:24:56PM +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> 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>

Applied to hyperv-next. Thanks.

Saurabh and Naman, I want to get this submitted in this merge window. If
you find any more issues with this patch, we can address them in the RC
phase. In the worst case, we can revert this patch later.

Wei