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

Helge Deller
2023-02-12T14:03:31Z

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...

> on both kernels and run that example. I do wonder if it's some O_DIRECT
> thing, does the example work if you just remove O_DIRECT from the file
> open?

No, still fails with O_DIRECT removed.

Thanks!
Helge