Hi, On Fri, Nov 14, 2025 at 08:05:55PM +0530, Naman Jain wrote: > > > On 11/14/2025 5:19 PM, Peter Morrow wrote: > > Hi Naman, > > > > On Fri, 14 Nov 2025 at 06:03, Naman Jain <[email protected]> > > 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/[email protected]/ > > > > > > > > > > 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. > > Hi Peter, > > Thanks for confirming. I am discussing this with Long Li, to hear his > thoughts on this, and have kept the patch ready. > Porting the same on 6.6 and older kernels would be a little different since > we don't have commit 547fa4ffd799 ("uio_hv_generic: Enable interrupt for low > speed VMBus devices") on these kernels and this would lead to merge > conflicts, which needs to be handled separately. > > Meanwhile, if I should be including any tags in the fix patch for debian > bug, please let me know.
Thank you very much for the quick analysis and fix. If you can add a Closes: https://bugs.debian.org/1120602 that would make our tracking for the fixes easier. But not sure if this is allowed for proposing the backport for a stable series, as it did not affect the upper releases. In any case your work is much appreciated! Regards, Salvatore
