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Message-ID: <7c9d143d9e70a9ff9b91fb5a55d8ba57bf1cc4f6.camel@siemens.com>
Date: Thu, 5 Feb 2026 14:09:51 +0000
From: "Bezdeka, Florian" <florian.bezdeka@...mens.com>
To: "kys@...rosoft.com" <kys@...rosoft.com>, "decui@...rosoft.com"
<decui@...rosoft.com>, "longli@...rosoft.com" <longli@...rosoft.com>,
"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
"wei.liu@...nel.org" <wei.liu@...nel.org>, "Kiszka, Jan"
<jan.kiszka@...mens.com>, "martin.petersen@...cle.com"
<martin.petersen@...cle.com>, "James.Bottomley@...senPartnership.com"
<James.Bottomley@...senPartnership.com>, "haiyangz@...rosoft.com"
<haiyangz@...rosoft.com>
CC: "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"levymitchell0@...il.com" <levymitchell0@...il.com>
Subject: Re: [PATCH] scsi: storvsc: Fix scheduling while atomic on PREEMPT_RT
On Thu, 2026-01-29 at 15:30 +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@...mens.com>
>
> This resolves the follow splat and lock-up when running with PREEMPT_RT
> enabled on Hyper-V:
>
> [ 415.140818] BUG: scheduling while atomic: stress-ng-iomix/1048/0x00000002
> [ 415.140822] INFO: lockdep is turned off.
> [ 415.140823] Modules linked in: intel_rapl_msr intel_rapl_common intel_uncore_frequency_common intel_pmc_core pmt_telemetry pmt_discovery pmt_class intel_pmc_ssram_telemetry intel_vsec ghash_clmulni_intel aesni_intel rapl binfmt_misc nls_ascii nls_cp437 vfat fat snd_pcm hyperv_drm snd_timer drm_client_lib drm_shmem_helper snd sg soundcore drm_kms_helper pcspkr hv_balloon hv_utils evdev joydev drm configfs efi_pstore nfnetlink vsock_loopback vmw_vsock_virtio_transport_common hv_sock vmw_vsock_vmci_transport vsock vmw_vmci efivarfs autofs4 ext4 crc16 mbcache jbd2 sr_mod sd_mod cdrom hv_storvsc serio_raw hid_generic scsi_transport_fc hid_hyperv scsi_mod hid hv_netvsc hyperv_keyboard scsi_common
> [ 415.140846] Preemption disabled at:
> [ 415.140847] [<ffffffffc0656171>] storvsc_queuecommand+0x2e1/0xbe0 [hv_storvsc]
> [ 415.140854] CPU: 8 UID: 0 PID: 1048 Comm: stress-ng-iomix Not tainted 6.19.0-rc7 #30 PREEMPT_{RT,(full)}
> [ 415.140856] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 09/04/2024
> [ 415.140857] Call Trace:
> [ 415.140861] <TASK>
> [ 415.140861] ? storvsc_queuecommand+0x2e1/0xbe0 [hv_storvsc]
> [ 415.140863] dump_stack_lvl+0x91/0xb0
> [ 415.140870] __schedule_bug+0x9c/0xc0
> [ 415.140875] __schedule+0xdf6/0x1300
> [ 415.140877] ? rtlock_slowlock_locked+0x56c/0x1980
> [ 415.140879] ? rcu_is_watching+0x12/0x60
> [ 415.140883] schedule_rtlock+0x21/0x40
> [ 415.140885] rtlock_slowlock_locked+0x502/0x1980
> [ 415.140891] rt_spin_lock+0x89/0x1e0
> [ 415.140893] hv_ringbuffer_write+0x87/0x2a0
> [ 415.140899] vmbus_sendpacket_mpb_desc+0xb6/0xe0
> [ 415.140900] ? rcu_is_watching+0x12/0x60
> [ 415.140902] storvsc_queuecommand+0x669/0xbe0 [hv_storvsc]
> [ 415.140904] ? HARDIRQ_verbose+0x10/0x10
> [ 415.140908] ? __rq_qos_issue+0x28/0x40
> [ 415.140911] scsi_queue_rq+0x760/0xd80 [scsi_mod]
> [ 415.140926] __blk_mq_issue_directly+0x4a/0xc0
> [ 415.140928] blk_mq_issue_direct+0x87/0x2b0
> [ 415.140931] blk_mq_dispatch_queue_requests+0x120/0x440
> [ 415.140933] blk_mq_flush_plug_list+0x7a/0x1a0
> [ 415.140935] __blk_flush_plug+0xf4/0x150
> [ 415.140940] __submit_bio+0x2b2/0x5c0
> [ 415.140944] ? submit_bio_noacct_nocheck+0x272/0x360
> [ 415.140946] submit_bio_noacct_nocheck+0x272/0x360
> [ 415.140951] ext4_read_bh_lock+0x3e/0x60 [ext4]
> [ 415.140995] ext4_block_write_begin+0x396/0x650 [ext4]
> [ 415.141018] ? __pfx_ext4_da_get_block_prep+0x10/0x10 [ext4]
> [ 415.141038] ext4_da_write_begin+0x1c4/0x350 [ext4]
> [ 415.141060] generic_perform_write+0x14e/0x2c0
> [ 415.141065] ext4_buffered_write_iter+0x6b/0x120 [ext4]
> [ 415.141083] vfs_write+0x2ca/0x570
> [ 415.141087] ksys_write+0x76/0xf0
> [ 415.141089] do_syscall_64+0x99/0x1490
> [ 415.141093] ? rcu_is_watching+0x12/0x60
> [ 415.141095] ? finish_task_switch.isra.0+0xdf/0x3d0
> [ 415.141097] ? rcu_is_watching+0x12/0x60
> [ 415.141098] ? lock_release+0x1f0/0x2a0
> [ 415.141100] ? rcu_is_watching+0x12/0x60
> [ 415.141101] ? finish_task_switch.isra.0+0xe4/0x3d0
> [ 415.141103] ? rcu_is_watching+0x12/0x60
> [ 415.141104] ? __schedule+0xb34/0x1300
> [ 415.141106] ? hrtimer_try_to_cancel+0x1d/0x170
> [ 415.141109] ? do_nanosleep+0x8b/0x160
> [ 415.141111] ? hrtimer_nanosleep+0x89/0x100
> [ 415.141114] ? __pfx_hrtimer_wakeup+0x10/0x10
> [ 415.141116] ? xfd_validate_state+0x26/0x90
> [ 415.141118] ? rcu_is_watching+0x12/0x60
> [ 415.141120] ? do_syscall_64+0x1e0/0x1490
> [ 415.141121] ? do_syscall_64+0x1e0/0x1490
> [ 415.141123] ? rcu_is_watching+0x12/0x60
> [ 415.141124] ? do_syscall_64+0x1e0/0x1490
> [ 415.141125] ? do_syscall_64+0x1e0/0x1490
> [ 415.141127] ? irqentry_exit+0x140/0x7e0
> [ 415.141129] entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> get_cpu() disables preemption while the spinlock hv_ringbuffer_write is
> using is converted to an rt-mutex under PREEMPT_RT.
Tested-by: Florian Bezdeka <florian.bezdeka@...mens.com>
>
> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> ---
This patch survived a 24h stress test with CONFIG_PREEMPT_RT enabled and
heavy load applied to the system.
Without this patch - and very same system configuration - the system
will lock up within 2 minutes.
Best regards,
Florian
--
Siemens AG, Foundational Technologies
Linux Expert Center
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