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

[Saurabh Singh Sengar]

On Wed, Feb 18, 2026 at 07:05:57AM +0000, Wei Liu wrote:
> On Mon, Feb 16, 2026 at 05:24:56PM +0100, Jan Kiszka wrote:
> > From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> > 
> > 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@xxxxxxxxxxx>
> 
> 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

I was in the process of completing the final round of testing; however, since
the change has now been merged, it will receive broader coverage, I will rely
on that.

Overall, the patch looks good to me.

- Saurabh