Re: Problem with smbdirect rw credits and initiator_depth

[Stefan Metzmacher <metze@samba.org>]

Am 15.12.25 um 21:17 schrieb Stefan Metzmacher:
> Am 14.12.25 um 23:56 schrieb Stefan Metzmacher:
>> Am 13.12.25 um 03:14 schrieb Namjae Jeon:
>>>> I've put these changes a long with rw credit fixes into my
>>>> for-6.18/ksmbd-smbdirect-regression-v4 branch, are you able to
>>>> test this?
>>> Problems still occur. See:
>>
>> :-( Would you be able to use rxe and cake a network capture?
>>
>> Using test files with all zeros, e.g.
>> dd if=/dev/zero of=/tmp/4096MBzeros-sparse.dat seek=4096MB bs=1 count=1
>> would allow gzip --best on the capture file to compress well...
> 
> I think I found something that explains it and
> I was able to reproduce and what I have in mind.
> 
> We increment recv_io.posted.count after ib_post_recv()
> 
> And manage_credits_prior_sending() uses
> 
> new_credits = recv_io.posted.count - recv_io.credits.count
> 
> But there is a race between the hardware receiving a message
> and recv_done being called in order to decrement recv_io.posted.count
> again. During that race manage_credits_prior_sending() might grant
> too much credits.
> 
> Please test my for-6.18/ksmbd-smbdirect-regression-v5 branch,
> I haven't tested this branch yet, I'm running out of time
> for the day.
> 
> But I tested it with smbclient and having a similar
> logic in fs/smb/common/smbdirect/smbdirect_connection.c

I was able to reproduce the problem and the fix I created
for-6.18/ksmbd-smbdirect-regression-v5 was not correct.

I needed to use

available = atomic_xchg(&sc->recv_io.credits.available, 0);

instead of

available = atomic_read(&sc->recv_io.credits.available);
atomic_sub(new_credits, &sc->recv_io.credits.available);

This following branch works for me:
for-6.18/ksmbd-smbdirect-regression-v7
and with the fixes again master this should also work:
for-6.19/ksmbd-smbdirect-regression-v1

I'll post real patches tomorrow.

Please check.

Thanks!
metze