[Samba] Samba 4.7.6-ubuntu taking 100% CPU

[Olaf Marzocchi]

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.

Cheers!
Olaf