Re: Using SQPOLL for-5.11/io_uring kernel NULL pointer dereference

[Pavel Begunkov <asml.silence@gmail.com>]

On 07/11/2020 14:09, Josef wrote:
>> I haven't got the first email, is it "kernel NULL pointer dereference"
>> as in the subject or just freeze?
> 
> that's weird..probably the size of the attached log file is too big...
> here dmesg log file
> https://gist.github.com/1Jo1/3d0bcefc18f097265f0dc1ef054a87c0

That's much better with the log, thanks! I'll take a look later

> 
>> - did you locate which test hangs it? If so what it uses? e.g. SQPOLL
>> sharing, IOPOLL., etc.
> 
> yes, it uses SQPOLL, without sharing, IPOLL is not enabled, and Async
> Flag is enabled
> 
>> - is it send/recvmsg, send/recv you use? any other?
> 
> no the tests which occurs the error use these operations: OP_READ,
> OP_WRITE, OP_POLL_ADD, OP_POLL_REMOVE, OP_CLOSE, OP_ACCEPT, OP_TIMEOUT
> (OP_READ, OP_WRITE and OP_CLOSE async flag is enabled)
> 
>> - does this happen often?
> 
> yeah quite often
> 
>> - you may try `funcgraph __io_sq_thread -H` or even with `io_sq_thread`
>> (funcgraph is from bpftools). Or catch that with some other tools.
> 
> I'm not quite familiar with these tools( kernel debugging in general)
> I'll take a look tomorrow

-- 
Pavel Begunkov