Hi Naman,
On Fri, 14 Nov 2025 at 06:03, Naman Jain <namjain@linux.microsoft.com> wrote:
On 11/13/2025 11:59 PM, Salvatore Bonaccorso wrote:
Peter Morrow reported in Debian a regression, reported in
https://bugs.debian.org/1120602 . The regression was seen after
updating, to 6.12.57-1 in Debian, but details on the offending commit
follows.
His report was as follows:
Dear Maintainer,
I'm seeing a kernel crash quite soon after boot on a debian trixie based
system running 6.12.57+deb13-amd64, unfortunately the kernel panics before
I can access the system to gather more information. Thus I'll provide details
of the system using a previously known good version. The panic is happening
100% of the time unfortunately. I have access to the serial console however
so can enable any required verbose logging during boot if necessary.
Crucially the crash is not seen with kernel version 6.12.41+deb13-amd64 with the
same userspace. We had pinned to that version until very recently to in order
to work around https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1109676
I'm running a dpdk application here (VPP) on Azure, VM form factor is a
"Standard DS3 v2 (4 vcpus, 14 GiB memory)".
The only relevant upstream commit in this area (as far as I can see) is:
https://lore.kernel.org/linux-hyperv/1bb599ee-fe28-409d-b430-2fc086268936@linux.microsoft.com/
The comment regarding avoiding races at start adds a bit more weight behind this
hunch, though it's only a hunch as I am most definitely nowhere near an expert
in this area.
-- Package-specific info:
[ 19.625535] BUG: kernel NULL pointer dereference, address: 00000000000000a0
[ 19.628874] #PF: supervisor read access in kernel mode
[ 19.630841] #PF: error_code(0x0000) - not-present page
[ 19.632788] PGD 0 P4D 0
[ 19.633905] Oops: Oops: 0000 [#1] PREEMPT SMP PTI
[ 19.635586] CPU: 3 UID: 0 PID: 0 Comm: swapper/3 Not tainted 6.12.57+deb13-amd64 #1 Debian 6.12.57-1
[ 19.640216] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 09/28/2024
[ 19.644514] RIP: 0010:hv_uio_channel_cb+0xd/0x20 [uio_hv_generic]
[ 19.646994] Code: 02 00 00 5b 5d e9 53 98 69 e9 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 8b 47 10 <48> 8b b8 a0 00 00 00 f0 83 44 24 fc 00 e9 51 6f fa ff 90 90 90 90
[ 19.654377] RSP: 0018:ffffb15ac01a4fa8 EFLAGS: 00010046
[ 19.656385] RAX: 0000000000000000 RBX: 0000000000000015 RCX: 0000000000000015
[ 19.659240] RDX: 0000000000000001 RSI: ffffffffffffffff RDI: ffff8ff69c759400
[ 19.662168] RBP: ffff8ff548790200 R08: ffff8ff548790200 R09: 00fca75150b080e9
[ 19.665239] R10: 0000000000000000 R11: ffffb15ac01a4ff8 R12: ffff8ff871dc1480
[ 19.668193] R13: ffff8ff69c759400 R14: ffff8ff69c7596a0 R15: ffffffffc106e160
[ 19.671106] FS: 0000000000000000(0000) GS:ffff8ff871d80000(0000) knlGS:0000000000000000
[ 19.674281] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 19.676533] CR2: 00000000000000a0 CR3: 0000000100ba6003 CR4: 00000000003706f0
[ 19.679385] Call Trace:
[ 19.680361] <IRQ>
[ 19.681181] vmbus_isr+0x1a5/0x210 [hv_vmbus]
[ 19.682916] __sysvec_hyperv_callback+0x32/0x60
[ 19.684991] sysvec_hyperv_callback+0x6c/0x90
[ 19.686665] </IRQ>
[ 19.687509] <TASK>
[ 19.688366] asm_sysvec_hyperv_callback+0x1a/0x20
[ 19.690262] RIP: 0010:pv_native_safe_halt+0xf/0x20
[ 19.692067] Code: 09 e9 c5 08 01 00 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d e5 3b 31 00 fb f4 <c3> cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90
[ 19.699119] RSP: 0018:ffffb15ac0103ed8 EFLAGS: 00000246
[ 19.701412] RAX: 0000000000000003 RBX: ffff8ff5403b1fc0 RCX: ffff8ff54c64ce30
[ 19.704328] RDX: 0000000000000000 RSI: 0000000000000003 RDI: 000000000001f894
[ 19.706910] RBP: 0000000000000003 R08: 000000000bb760d9 R09: 00fca75150b080e9
[ 19.709762] R10: 0000000000000003 R11: 0000000000000001 R12: 0000000000000000
[ 19.712510] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[ 19.715173] default_idle+0x9/0x20
[ 19.716846] default_idle_call+0x29/0x100
[ 19.718623] do_idle+0x1fe/0x240
[ 19.720045] cpu_startup_entry+0x29/0x30
[ 19.721595] start_secondary+0x11e/0x140
[ 19.723080] common_startup_64+0x13e/0x141
[ 19.725222] </TASK>
[ 19.726387] Modules linked in: isofs cdrom uio_hv_generic uio binfmt_misc intel_rapl_msr intel_rapl_common intel_uncore_frequency_common isst_if_mbox_msr isst_if_common rpcrdma skx_edac_common nfit sunrpc libnvdimm crct10dif_pclmul ghash_clmulni_intel sha512_ssse3 sha256_ssse3 rdma_ucm ib_iser sha1_ssse3 rdma_cm aesni_intel iw_cm gf128mul crypto_simd libiscsi cryptd ib_umad ib_ipoib scsi_transport_iscsi ib_cm rapl sg hv_utils hv_balloon evdev pcspkr joydev mpls_router ip_tunnel ramoops configfs pstore_blk efi_pstore pstore_zone nfnetlink vsock_loopback vmw_vsock_virtio_transport_common hv_sock vmw_vsock_vmci_transport vsock vmw_vmci efivarfs ip_tables x_tables autofs4 overlay squashfs dm_verity dm_bufio reed_solomon dm_mod loop ext4 crc16 mbcache jbd2 crc32c_generic mlx5_ib ib_uverbs ib_core mlx5_core mlxfw pci_hyperv pci_hyperv_intf hyperv_drm drm_shmem_helper sd_mod drm_kms_helper hv_storvsc scsi_transport_fc drm scsi_mod hid_generic hid_hyperv hid serio_raw hv_netvsc hyperv_keyboard scsi_common hv_vmbus
[ 19.726466] crc32_pclmul crc32c_intel
[ 19.765771] CR2: 00000000000000a0
[ 19.767524] ---[ end trace 0000000000000000 ]---
[ 19.800433] RIP: 0010:hv_uio_channel_cb+0xd/0x20 [uio_hv_generic]
[ 19.803170] Code: 02 00 00 5b 5d e9 53 98 69 e9 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 8b 47 10 <48> 8b b8 a0 00 00 00 f0 83 44 24 fc 00 e9 51 6f fa ff 90 90 90 90
[ 19.811041] RSP: 0018:ffffb15ac01a4fa8 EFLAGS: 00010046
[ 19.813466] RAX: 0000000000000000 RBX: 0000000000000015 RCX: 0000000000000015
[ 19.816504] RDX: 0000000000000001 RSI: ffffffffffffffff RDI: ffff8ff69c759400
[ 19.819484] RBP: ffff8ff548790200 R08: ffff8ff548790200 R09: 00fca75150b080e9
[ 19.822625] R10: 0000000000000000 R11: ffffb15ac01a4ff8 R12: ffff8ff871dc1480
[ 19.825569] R13: ffff8ff69c759400 R14: ffff8ff69c7596a0 R15: ffffffffc106e160
[ 19.828804] FS: 0000000000000000(0000) GS:ffff8ff871d80000(0000) knlGS:0000000000000000
[ 19.832214] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 19.834709] CR2: 00000000000000a0 CR3: 0000000100ba6003 CR4: 00000000003706f0
[ 19.837976] Kernel panic - not syncing: Fatal exception in interrupt
[ 19.841825] Kernel Offset: 0x28a00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[ 19.896620] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---
<snip>
The offending commit appers to be the backport of b15b7d2a1b09
("uio_hv_generic: Let userspace take care of interrupt mask") for
6.12.y.
Peter confirmed that reverting this commit on top of 6.12.57-1 as
packaged in Debian resolves indeed the issue. Interestingly the issue
is *not* seen with 6.17.7 based kernel in Debian.
#regzbot introduced: 37bd91f22794dc05436130d6983302cb90ecfe7e
#regzbot monitor: https://bugs.debian.org/1120602
Thank you already!
Regards,
Salvatore
Hi Peter, Salvatore,
Thanks for reporting this crash, and sorry for the trouble. Here is my
analysis.
On 6.17.7, where commit d062463edf17 ("uio_hv_generic: Set event for all
channels on the device") is present, hv_uio_irqcontrol() supports
setting of interrupt mask from userspace for sub-channels as well.
This aligns with commit e29587c07537 ("uio_hv_generic: Let userspace
take care of interrupt mask") which relies on userspace to manage
interrupt mask, so it safely removes the interrupt mask management logic
in the driver.
However, in 6.12.57, the first commit is not present, but the second one
is, so there is no way to disable interrupt mask for sub-channels and
interrupt_mask stays 0, which means interrupts are not masked. So we may
be having an interrupt callback being handled for a sub-channel, where
we do not expect it to come. This may be causing this issue.
This would have led to a crash in hv_uio_channel_cb() for sub-channels:
struct hv_device *hv_dev = chan->device_obj;
I have ported commit d062463edf17 ("uio_hv_generic: Set event for all
channels on the device") on 6.12.57, and resolved some merge conflicts.
Could you please help with testing this, if it works for you.
Applying the patch against the debian 6.12.57 kernel worked, I am no
longer seeing that panic on boot:
gnos@vEdge:~$ uname -a
Linux vEdge 6.12+unreleased-amd64 #1 SMP PREEMPT_DYNAMIC Debian
6.12.57-1a~test (2025-11-14) x86_64 GNU/Linux
gnos@vEdge:~$ uptime
11:46:33 up 4 min, 1 user, load average: 3.31, 2.07, 0.89
gnos@vEdge:~$ sudo dmidecode -t system
# dmidecode 3.6
Getting SMBIOS data from sysfs.
SMBIOS 3.1.0 present.
Handle 0x0001, DMI type 1, 27 bytes
System Information
Manufacturer: Microsoft Corporation
Product Name: Virtual Machine
Version: Hyper-V UEFI Release v4.1
Serial Number: 0000-0002-8036-1108-7588-3134-50
UUID: 26e86d6e-140c-496a-862c-a3b3bbcd16ad
Wake-up Type: Power Switch
SKU Number: None
Family: Virtual Machine
Handle 0x0010, DMI type 32, 11 bytes
System Boot Information
Status: No errors detected
gnos@vEdge:~$
Thanks a lot for the quick analysis!
Peter.