From: Jan Kiszka <[email protected]>
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.
Signed-off-by: Jan Kiszka <[email protected]>
---
This is likely just the tip of an iceberg, see specifically [1], but if
you never start addressing it, it will continue to crash ships, even if
those are only on test cruises (we are fully aware that Hyper-V provides
no RT guarantees for guests). A pragmatic alternative to that would be a
simple
config HYPERV
depends on !PREEMPT_RT
Please share your thoughts if this fix is worth it, or if we should
better stop looking at the next splats that show up after it. We are
currently considering to thread some of the hv platform IRQs under
PREEMPT_RT as potential next step.
TIA!
[1]
https://lore.kernel.org/all/[email protected]/
drivers/scsi/storvsc_drv.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index b43d876747b7..68c837146b9e 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1855,8 +1855,9 @@ static int storvsc_queuecommand(struct Scsi_Host *host,
struct scsi_cmnd *scmnd)
cmd_request->payload_sz = payload_sz;
/* Invokes the vsc to start an IO */
- ret = storvsc_do_io(dev, cmd_request, get_cpu());
- put_cpu();
+ migrate_disable();
+ ret = storvsc_do_io(dev, cmd_request, smp_processor_id());
+ migrate_enable();
if (ret)
scsi_dma_unmap(scmnd);
--
2.51.0
