[Samba] Samba 4.7.6-ubuntu taking 100% CPU

[Jeremy Allison]

On Fri, Apr 02, 2021 at 11:16:10PM +0200, Olaf Marzocchi via samba wrote:
>
>
>Il 02/04/2021 23:04, Jeremy Allison ha scritto:
>>On Fri, Apr 02, 2021 at 06:56:47PM +0200, Olaf Marzocchi via samba wrote:
>>>Dear all,
>>>I already sent this email but I wrongly added attachments, 
>>>resulting in the first email being rejected. Sorry if you read the 
>>>followup with ZFS properties.
>>>I'm sending it again using external storage where needed.
>>>
>>>I recently incurred in an issue with Samba 4.7.6-ubuntu (Ubuntu 
>>>18.04.05 LTS, with latest updates).
>>>I'm not sure what caused the issue, since at the same time I 
>>>performed updates to Ubuntu (apt upgrade) and I separately updated 
>>>the zfs kernel module to 2.0.4 from whatever version available mid 
>>>last year, also some time passed before I noticed the present 
>>>issue.
>>>
>>>The issue manifests itself as following: when I try to open some 
>>>files (not all of them) from any SMB share (I tried two different 
>>>Windows 10 machines and one macOS 10.14), the smb3 process takes 
>>>100% CPU, it doesn't seem to retrieve the file, and I have to kill 
>>>it "-9", the hard way. I found that, sometimes, after I kill smbd3 
>>>Windows gets the file I tried to open, but it's not a way that 
>>>always works: sometimes it's corrupted (cut too short).
>>>I tested locally from ssh and the same files have no issues 
>>>whatsoever, it's not a hardware issue. I can read and copy them 
>>>without problems.
>>
>>Use strace -p <spinning process id> to get system call
>>traces to see what is going on.
>
>Thanks for the reply!
>I tried just now:
>
>sendfile(36, 30, [360448], 262144)      = -1 EAGAIN (Resource 
>temporarily unavailable)
>
>I disabled sendfile and the issue is solved.
>I'm very thankful for the help!
>
>I tried transferring some big files and I still saturate gigabit, 
>while smaller files are disk-limited anyway. It doesn't look like I 
>actually need sendfile active.
>
>I'll investigate the sendfile issue with recent ZFS and if needed I'll 
>report it on their mailing list.
>

Hmmm. That may be an old bug (Samba 4.7.6 is quite old
now) when using sendfile() with non-blocking sockets.

It might not be sendfile, but Samba here. I'd advise
trying a later Samba version.