Re: io_uring failure on parisc (32-bit userspace and 64-bit kernel)

Helge Deller
2023-02-12T19:35:29Z

On 2/12/23 15:03, Helge Deller wrote:
> On 2/12/23 14:35, Jens Axboe wrote:
>> On 2/12/23 6:28?AM, Helge Deller wrote:
>>> On 2/12/23 14:16, Jens Axboe wrote:
>>>> On 2/12/23 2:47?AM, Helge Deller wrote:
>>>>> Hi all,
>>>>>
>>>>> We see io-uring failures on the parisc architecture with this testcase:
>>>>> https://github.com/axboe/liburing/blob/master/examples/io_uring-test.c
>>>>>
>>>>> parisc is always big-endian 32-bit userspace, with either 32- or 64-bit kernel.
>>>>>
>>>>> On a 64-bit kernel (6.1.11):
>>>>> deller@parisc:~$ ./io_uring-test test.file
>>>>> ret=0, wanted 4096
>>>>> Submitted=4, completed=1, bytes=0
>>>>> -> failure
>>>>>
>>>>> strace shows:
>>>>> io_uring_setup(4, {flags=0, sq_thread_cpu=0, sq_thread_idle=0, sq_entries=4, cq_entries=8, features=IORING_FEAT_SINGLE_MMAP|IORING_FEAT_NODROP|IORING_FEAT_SUBMIT_STABLE|IORING_FEAT_RW_CUR_POS|IORING_FEAT_CUR_PERSONALITY|IORING_FEAT_FAST_POLL|IORING_FEAT_POLL_32BITS|0x1f80, sq_off={head=0, tail=16, ring_mask=64, ring_entries=72, flags=84, dropped=80, array=224}, cq_off={head=32, tail=48, ring_mask=68, ring_entries=76, overflow=92, cqes=96, flags=0x58 /* IORING_CQ_??? */}}) = 3
>>>>> mmap2(NULL, 240, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_POPULATE, 3, 0) = 0xf7522000
>>>>> mmap2(NULL, 256, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_POPULATE, 3, 0x10000000) = 0xf6922000
>>>>> openat(AT_FDCWD, "libell0-dbgsym_0.56-2_hppa.deb", O_RDONLY|O_DIRECT) = 4
>>>>> statx(4, "", AT_STATX_SYNC_AS_STAT|AT_NO_AUTOMOUNT|AT_EMPTY_PATH, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0644, stx_size=689308, ...}) = 0
>>>>> getrandom("\x5c\xcf\x38\x2d", 4, GRND_NONBLOCK) = 4
>>>>> brk(NULL)                               = 0x4ae000
>>>>> brk(0x4cf000)                           = 0x4cf000
>>>>> io_uring_enter(3, 4, 0, 0, NULL, 8)     = 0
>>>>>
>>>>>
>>>>> Running the same testcase on a 32-bit kernel (6.1.11) works:
>>>>> root@debian:~# ./io_uring-test test.file
>>>>> Submitted=4, completed=4, bytes=16384
>>>>> -> ok.
>>>>>
>>>>> strace:
>>>>> io_uring_setup(4, {flags=0, sq_thread_cpu=0, sq_thread_idle=0, sq_entries=4, cq_entries=8, features=IORING_FEAT_SINGLE_MMAP|IORING_FEAT_NODROP|IORING_FEAT_SUBMIT_STABLE|IORING_FEAT_RW_CUR_POS|IORING_FEAT_CUR_PERSONALITY|IORING_FEAT_FAST_POLL|IORING_FEAT_POLL_32BITS|0x1f80, sq_off={head=0, tail=16, ring_mask=64, ring_entries=72, flags=84, dropped=80, array=224}, cq_off={head=32, tail=48, ring_mask=68, ring_entries=76, overflow=92, cqes=96, flags=0x58 /* IORING_CQ_??? */}}) = 3
>>>>> mmap2(NULL, 240, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_POPULATE, 3, 0) = 0xf6d4c000
>>>>> mmap2(NULL, 256, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_POPULATE, 3, 0x10000000) = 0xf694c000
>>>>> openat(AT_FDCWD, "trace.dat", O_RDONLY|O_DIRECT) = 4
>>>>> statx(4, "", AT_STATX_SYNC_AS_STAT|AT_NO_AUTOMOUNT|AT_EMPTY_PATH, STATX_BASIC_STATS, {stx_mask=STATX_BASIC_STATS|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0644, stx_size=1855488, ...}) = 0
>>>>> getrandom("\xb2\x3f\x0c\x65", 4, GRND_NONBLOCK) = 4
>>>>> brk(NULL)                               = 0x15000
>>>>> brk(0x36000)                            = 0x36000
>>>>> io_uring_enter(3, 4, 0, 0, NULL, 8)     = 4
>>>>>
>>>>> I'm happy to test any patch if someone has an idea....
>>>>
>>>> No idea what this could be, to be honest. I tried your qemu vm image,
>>>> and it does boot, but it's missing keys to be able to update apt and
>>>> install packages... After fiddling with this for 30 min I gave up, any
>>>> chance you can update the sid image? Given how slow this thing is
>>>> running, it'd take me all day to do a fresh install and I have to admit
>>>> I'm not THAT motivated about parisc to do that :)
>>>
>>> Yes, I will update that image, but qemu currently only supports a
>>> 32-bit PA-RISC CPU which can only run the 32-bit kernel. So even if I
>>> update it, you won't be able to reproduce it, as it only happens with
>>> the 64-bit kernel. I'm sure it's some kind of missing 32-to-64bit
>>> translation in the kernel, which triggers only big-endian machines.
>>
>> I built my own kernel for it, so that should be fine, correct?
>
> No, as qemu won't boot the 64-bit kernel.
>
>> We'll see soon enough, managed to disable enough checks on the
>> debian-10 image to actually make it install packages.
>>
>>> Does powerpc with a 64-bit ppc64 kernel work?
>>> I'd assume it will show the same issue.
>>
>> No idea... Only stuff I use and test on is x86-64/32 and arm64.
>
> Would be interesting if someone could test...
>
>>> I will try to add some printks and compare the output of 32- and
>>> 64-bit kernels. If you have some suggestion where to add such (which?)
>>> debug code, it would help me a lot.
>>
>> I'd just try:
>>
>> echo 1 > /sys/kernel/debug/tracing/events/io_uring
>
> I'll try, but will take some time...
>

At entry of io_submit_sqes(), io_sqring_entries() returns 0, because
ctx->rings->sq.tail is 0 (wrongly on broken 64-bit, but ok value 4 on 32-bit), and
ctx->cached_sq_head is 0 in both cases.

Helge