samba - Jul 2004 - Antwort: Re: 3.0.4: smbd's + nscd's = 100% CPU; load > 4

>> Bingo! It is exactly the same case.
>> Two user names were spelled out slightly wrong
>> in the /etc/group. As a consequence,
>> under certain circumstances the "smbd" process
>> keeps trying to resolve the name and doesn't
>> take "no" from "nscd" for an answer.
>> Each "smbd" process is looping around
>> these 5 system calls:
>> 1) create a socket,
>> 2) connect to nscd's socket,
>> 3) write the mis-spelled name,
>> 4) read negative answer
>> 5) close socket:
>>
>>    socket(PF_UNIX,SOCK_STREAM,0)=26
>>   
connect(26,{sa_family=AF_UNIX,path="/var/run/.nscd_socket"},110)=0
>>   
writev(26,[{"\2\0...\0\22\0...",12},{"GeorgeDubbyaBusch\0",18}],2)=30
>>    read(26,"\2\0\0\...\0\377\377\377\377\377\377"...,36)=36
>>    close(26)=0
>>
>> and the nscds spin like this
>>
>>    poll({fd=3,events=POLLRDNORM,revents=POLLRDNORM}],1,-1)=1
>>    accept(3,,NULL)=9
>>    read(9,"\2\0\0\0\0\0\0\0\22\0\0\0",12)=12
>>    read(9,"GeorgeDubbyaBusch\0",18)=18
>>    write(9,"\2\0\...\0\377\377\377\377\377\377"...,36=36
>>    close(9)=0
>>
>> Since both mis-spelled names are among the
>> earliest user names in 2 most frequently used
>> groups (one is "users"), it's hard to tell
>> why the smbd processes spin out of control so
>> infrequently. Jeremy will know more about that.
>
> Ok, looking at the code in 3.0 there is no loop around the
> lookup for a bad user name. The code in question is here:
>
>     for (gr = grp->gr_mem; (*gr != NULL) && ((*gr)[0] !=
'\0'); gr += 1)
{
>           struct passwd *pw = getpwnam(*gr);
>
>           if (pw == NULL)
>                 continue;
>           add_uid_to_array_unique(pw->pw_uid, uids, num);
> }
>
> Note that if pw == NULL then the name should be skipped and
> the next entry examined. This code is not looping on bad lookups
> within smbd.
>
> Is it possible to attach to the smbd in question with gdb and
> walk through this code with a bad username in the group entry
> list and see if the getpwnam call ever returns NULL or just
> loops inside glibc ?
I checked my /etc/group for irregular entries and repaired
all of them. Since then the problem didn't occur any more.
Even so it wasn't very frequent.

I still have a bunch of strace logs of smbd and of nscd.
Cann I upload it somewhere for you if you can use it?

Or do you suggest to replant the erroneous entries and
wait for the loop ?

Cheers

---------

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----------

On Tue, Jul 13, 2004 at 07:52:30PM +0200, Dragan.Krnic@bahn.de
wrote:
> 
> I checked my /etc/group for irregular entries and repaired
> all of them. Since then the problem didn't occur any more.
> Even so it wasn't very frequent.
> 
> I still have a bunch of strace logs of smbd and of nscd.
> Cann I upload it somewhere for you if you can use it?
> 
> Or do you suggest to replant the erroneous entries and
> wait for the loop ?
Actually if you could add one erroneous entry and catch it
in gdb in the act of looping that would be very helpful. I'm
still trying to determine if the bug is in glibc or smbd.

Thanks,

	Jeremy.