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

Helge Deller <deller@xxxxxx> · Sun, 12 Feb 2023 14:28:02 +0100

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.

Does powerpc with a 64-bit ppc64 kernel work?
I'd assume it will show the same issue.

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.

Thank you,
Helge