Re: io_uring failure on parisc with VIPT caches

[Jens Axboe <axboe@kernel.dk>]

On 2/15/23 2:06 PM, John David Anglin wrote:
> On 2023-02-15 3:37 p.m., Jens Axboe wrote:
>>> System crashes running test buf-ring.t.
>> Huh, what's the crash?
> Not much info.  System log indicates an HPMC occurred. Unfortunately, recovery code doesn't work.
>>
>>> Running test buf-ring.t bad run 0/0 = -233
>> THis one, and the similar -223 ones, you need to try and dig into that.
>> It doesn't reproduce for me, and it very much seems like the test case
>> having a different view of what -ENOBUFS looks like and hence it fails
>> when the kernel passes down something that is -ENOBUFS internally, but
>> doesn't match the app -ENOBUFS value. Are you running a 64-bit kernel?
>> Would that cause any differences?
> I'm running a 64-bit kernel (6.1.12).
> 
> I believe 32 and 64-bit kernels have same error codes.
> 
> I see three places in io_uring where -ENOBUFS is returned.  They have similar code:
> 
> retry_multishot:
>         if (io_do_buffer_select(req)) {
>                 void __user *buf;
>                 size_t len = sr->len;
> 
>                 buf = io_buffer_select(req, &len, issue_flags);
>                 if (!buf)
>                         return -ENOBUFS;

buf-ring is using a kernel mapped user ring, so may indeed be the same
kind of coloring issue that we saw with the main rings.

-- 
Jens Axboe