On Tue, 2026-02-03 at 17:01 +0100, Jan Kiszka wrote: > 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 complete vmbus_handler 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. > > Signed-off-by: Jan Kiszka <[email protected]>
Tested-by: Florian Bezdeka <[email protected]> This patch survived a 24h stress test with CONFIG_PREEMPT_RT enabled and heavy load applied to the system. There was no lockup happening without this patch. The lockdep warning is gone now. Best regards, Florian -- Siemens AG, Foundational Technologies Linux Expert Center
