Hi Jens,
Kevin Lumik reported in Debian the following issue (not exactly a minimal reproducer, but bisection results follows):
On Fri, Sep 26, 2025 at 10:34:22AM +0300, Kevin Lumik wrote:
Dear Maintainer,
After upgrading from Debian Bookworm to Trixie, an issue within KVM guests when creating an LVM snapshot of its volume has surfaced. When a LVM snapshot is taken from the host, the guest starts to get I/O errors. The issue seems to only appear when aio=io_uring is specified in the KVM drive parameters and also seems to resolve when downgrading the kernel package down to 6.1. The issue is also not reproducible when using aio=native.
KVM args for the drive: "-drive id=drive- virtio0,format=raw,file=/dev/dom/vps_testsql,cache=none,aio=io_uring,index=0,media=disk,if=virtio"
An IO workload is being created in the VM using "fio --randrepeat=1 --ioengine=io_uring --direct=1 --gtod_reduce=1 -- name=randwrite --filename=/root/test.bin --bs=4k --iodepth=64 --runtime=60 --numjobs=32 --readwrite=randwrite --size=1G --rwmixread=75 --group_reporting"
After running "lvcreate -s /dev/dom/vps_testsql -n test -L 1G" on the host we can observe fio erroring out:
... fio: io_u error on file /root/test.bin: Input/output error: write offset=46977024, buflen=4096 fio: pid=7367, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: io_u error on file /root/test.bin: Input/output error: write offset=261505024, buflen=4096 fio: pid=7374, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: io_u error on file /root/test.bin: Input/output error: write offset=973840384, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=9637888, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=159965184, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=857505792, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=90787840, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=26427392, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=955621376, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=96169984, buflen=4096 fio: pid=7372, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: pid=7362, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: io_u error on file /root/test.bin: Input/output error: write offset=203702272, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=814649344, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=91467776, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=948256768, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=105295872, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=75247616, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=1062293504, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=111955968, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=942563328, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=117354496, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=1050402816, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=125419520, buflen=4096 fio: io_u error on file /root/test.bin: Input/output error: write offset=129044480, buflen=4096 fio: pid=7369, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: pid=7373, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: pid=7348, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: pid=7375, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: pid=7358, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error fio: pid=7359, err=5/file:io_u.c:1876, func=io_u error, error=Input/output error
randwrite: (groupid=0, jobs=32): err= 5 (file:io_u.c:1876, func=io_u error, error=Input/output error): pid=7344: Thu Sep 25 16:28:30 2025 write: IOPS=194k, BW=758MiB/s (795MB/s)(3976MiB/5244msec); 0 zone resets bw ( KiB/s): min=657104, max=1009816, per=100.00%, avg=785345.80, stdev=4331.73, samples=320 iops : min=164276, max=252454, avg=196336.40, stdev=1082.93, samples=320 cpu : usr=0.33%, sys=1.07%, ctx=18912, majf=0, minf=455 IO depths : 1=0.1%, 2=0.1%, 4=0.1%, 8=0.1%, 16=0.1%, 32=0.1%, >=64=99.8% submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0% complete : 0=0.1%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.1%, >=64=0.0% issued rwts: total=0,1019955,0,0 short=0,0,0,0 dropped=0,0,0,0 latency : target=0, window=0, percentile=100.00%, depth=64
Run status group 0 (all jobs): WRITE: bw=758MiB/s (795MB/s), 758MiB/s-758MiB/s (795MB/s-795MB/s), io=3976MiB (4169MB), run=5244-5244msec
Disk stats (read/write): vda: ios=1/1001361, merge=0/2, ticks=0/10314531, in_queue=10314549, util=97.82% Bus error
And the error is also visible in the kernel error log of the VM: [ 361.962970] I/O error, dev vda, sector 83277192 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.963945] I/O error, dev vda, sector 83067480 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964489] I/O error, dev vda, sector 82881208 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964499] I/O error, dev vda, sector 83031976 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964501] I/O error, dev vda, sector 83089832 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964503] I/O error, dev vda, sector 83156184 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964522] I/O error, dev vda, sector 83183384 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964524] I/O error, dev vda, sector 83310704 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964525] I/O error, dev vda, sector 83311144 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2 [ 361.964532] I/O error, dev vda, sector 83315272 op 0x1:(WRITE) flags 0x8800 phys_seg 1 prio class 2
The host does not generate any erros, they only seem to occur within the VM.
Now I asked Kevin if a bisection is possible, and the following results was found (https://bugs.debian.org/1116358#41):
I've identified the first bad commit using git bisect:
90bfb28d5fa8127a113a140c9791ea0b40ab156a is the first bad commit commit 90bfb28d5fa8127a113a140c9791ea0b40ab156a Author: Jens Axboe axboe@kernel.dk Date: Tue Sep 10 08:57:04 2024 -0600
io_uring/rw: drop -EOPNOTSUPP check in __io_complete_rw_common()
A recent change ensured that the necessary -EOPNOTSUPP -> -EAGAIN transformation happens inline on both the reader and writer side, and hence there's no need to check for both of these anymore on the completion handler side.
Signed-off-by: Jens Axboe axboe@kernel.dk
io_uring/rw.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
Here is the git bisect log as well:
git bisect start # status: waiting for both good and bad commits # good: [98f7e32f20d28ec452afb208f9cffc08448a2652] Linux 6.11 git bisect good 98f7e32f20d28ec452afb208f9cffc08448a2652 # status: waiting for bad commit, 1 good commit known # bad: [59b723cd2adbac2a34fc8e12c74ae26ae45bf230] Linux 6.12-rc6 git bisect bad 59b723cd2adbac2a34fc8e12c74ae26ae45bf230 # bad: [de848da12f752170c2ebe114804a985314fd5a6a] Merge tag 'drm-next-2024-09-19' of https://gitlab.freedesktop.org/drm/kernel git bisect bad de848da12f752170c2ebe114804a985314fd5a6a # bad: [7b17f5ebd5fc5e9275eaa5af3d0771f2a7b01bbf] Merge tag 'soc-dt-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc git bisect bad 7b17f5ebd5fc5e9275eaa5af3d0771f2a7b01bbf # good: [64dd3b6a79f0907d36de481b0f15fab323a53e5a] Merge tag 'for-linus-non-x86' of git://git.kernel.org/pub/scm/virt/kvm/kvm git bisect good 64dd3b6a79f0907d36de481b0f15fab323a53e5a # bad: [daa394f0f9d3cb002c72e2d3db99972e2ee42862] Merge tag 'core-debugobjects-2024-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip git bisect bad daa394f0f9d3cb002c72e2d3db99972e2ee42862 # good: [effdcd5275ed645f6e0f8e8ce690b97795722197] Merge tag 'affs-for-6.12-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux git bisect good effdcd5275ed645f6e0f8e8ce690b97795722197 # bad: [26bb0d3f38a764b743a3ad5c8b6e5b5044d7ceb4] Merge tag 'for-6.12/block-20240913' of git://git.kernel.dk/linux git bisect bad 26bb0d3f38a764b743a3ad5c8b6e5b5044d7ceb4 # bad: [3a4d319a8fb5a9bbdf5b31ef32841eb286b1dcc2] Merge tag 'for-6.12/io_uring-20240913' of git://git.kernel.dk/linux git bisect bad 3a4d319a8fb5a9bbdf5b31ef32841eb286b1dcc2 # good: [df2825e98507d10cb037a308087ecd7cb3f6688d] btrfs: always pass readahead state to defrag git bisect good df2825e98507d10cb037a308087ecd7cb3f6688d # good: [69a3a0a45a2f72412c2ba31761cc9193bb746fef] Merge tag 'erofs-for-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs git bisect good 69a3a0a45a2f72412c2ba31761cc9193bb746fef # good: [ecd5c9b29643f383d39320e30d21b8615bd893da] io_uring/kbuf: add io_kbuf_commit() helper git bisect good ecd5c9b29643f383d39320e30d21b8615bd893da # good: [f011c9cf04c06f16b24f583d313d3c012e589e50] io_uring/sqpoll: do not allow pinning outside of cpuset git bisect good f011c9cf04c06f16b24f583d313d3c012e589e50 # bad: [84eacf177faa605853c58e5b1c0d9544b88c16fd] io_uring/io-wq: inherit cpuset of cgroup in io worker git bisect bad 84eacf177faa605853c58e5b1c0d9544b88c16fd # bad: [90bfb28d5fa8127a113a140c9791ea0b40ab156a] io_uring/rw: drop - EOPNOTSUPP check in __io_complete_rw_common() git bisect bad 90bfb28d5fa8127a113a140c9791ea0b40ab156a # good: [c0a9d496e0fece67db777bd48550376cf2960c47] io_uring/rw: treat - EOPNOTSUPP for IOCB_NOWAIT like -EAGAIN git bisect good c0a9d496e0fece67db777bd48550376cf2960c47 # first bad commit: [90bfb28d5fa8127a113a140c9791ea0b40ab156a] io_uring/rw: drop -EOPNOTSUPP check in __io_complete_rw_common()
#regzbot introduced: 90bfb28d5fa8127a113a140c9791ea0b40ab156a #regzbot link: https://bugs.debian.org/1116358
Does thi ring any bell?
Regards, Salvatore