smbd holds 70% cpu

[Nir Livni]

Anthony Liguori wrote:


> > And Linux gurus, what the heck is ERESTARTNOHAND? I
> > can't find it in /usr/include... I did find ERESTART,
> > which is standard...
>
> ERESTARTNOHAND is a kernel specific errno (in a kernel tree look for
> include/linux/errno.h).  ERESTARTNOHAND signals the caller that they
> should restart if there is no handler.  A userspace app should never see
> this (I don't know if it's even supposed to show up at the libc level).
>
> This leads to an interesting question, if libc is looping hard on select
> w/ERESTARTNOHAND then perhaps the loop is in libc (which seems unlikely).
> I think a better thing than strace would be to kill -SEGV the process when
> it's looping hard and see what the back trace is.

I do recall that I tried to gdb this process. I don't think I saw something
special other that the select and/or sys_select functions. I would have
remembered ...

This phenomenan has not (yet) been reproduced.

Are there any known kernel problems with select/poll in version 2.4.18-14 ?

> Anthony Liguori
> Linux/Active Directory Interoperability
> Linux Technology Center (LTC) - IBM Austin
> E-mail: aliguor at us.ibm.com
> Phone: (512) 838-1208
> Tie Line: 678-1208
>
>
>
>
> David Collier-Brown -- Customer Engineering <David.Collier-Brown at Sun.COM>
> Sent by: samba-technical-bounces+aliguor=us.ibm.com at lists.samba.org
> 31/07/2003 08:36 AM
>
>
>         To:     Nir Livni <nirl at cyber-ark.com>
>         cc:     samba-technical at samba.org
>         Subject:        Re: smbd holds 70% cpu
>
>
>
> Nir Livni wrote:
> >>int select(int  nfds,  fd_set  *readfds,  fd_set  *writefds,
> >>       fd_set *errorfds, struct timeval *timeout);
> >>
> >>               Firstly, see how often it's happening, either by
> >>               reading the contents of the timeval or just counting
> >>               seconds (;-))
> >>
> >>               Next llok at the return value: -1 for an error (check
> errno)
> >>               0 for a timeout, and a non-zero number if at elast one
> >>               fd reorted something.
> >>
> >
> >
> > Does this one look like a reasonable select ?
> > select(1024, [29 30], NULL, NULL, NULL) = ? ERESTARTNOHAND (To be
> > restarted).
>
>                  Ok, it's saying that FDs 29 and 30 have data,
>                  but it returned -1 and errno == ERESTARTNOHAND
>
>                  LSOF will tell you what 29 and 30 are, but
>                  the interesting thing is ERESTARTNOHAND...
>                  The standard says that legal errnos are
>                  EBADF, EINTR and EINVAL, and glibc adds ENOMEM.
>
>                  Looking at the code, the select calls are
> C symbol: select
>
>    File        Function   Line
> 1 types.h     <global>    94 #define select _abi_select
> 6 select.c    sys_select  94 ret =
>                   select(maxfd,readfds2,writefds,errorfds,tval);
> 7 system.c    sys_usleep  71 select(0,NULL,NULL,NULL,&tval);
> 1 wb_common.c write_sock 200 if (select(winbindd_fd + 1, &r_fds,
>                   NULL, NULL, &tv) == -1) {
>
>                  The likely (but not guaranteed) call is in sys_select,
>                  which passes a timeval of 0 instead of NULL...
>
>                  Ok, samba gurus, assuming this looping was in sys_select,
>                  what would happen if errno was set to something
> unexpected?
>
>                  And Linux gurus, what the heck is ERESTARTNOHAND? I
>                  can't find it in /usr/include... I did find ERESTART,
>                  which is standard...
>
> --dave
> --
> David Collier-Brown,           | Always do right. This will gratify
> Sun Microsystems DCMO          | some people and astonish the rest.
> Toronto, Ontario               |
> (905) 415-2849 or x52849       | davecb at canada.sun.com
>
>
>
>
>