Re: deadlock in signal handler with NPTL

[Thorsten Kukuk <kukuk@suse.de>]

On Tue, Jun 22, Steve Munroe wrote:

> Thorsten Kukuk <kukuk@suse.de> wrote on 06/22/2004 11:22:56 PM:
> 
> > On Tue, Jun 22, Jakub Jelinek wrote:
> >
> > > On Tue, Jun 22, 2004 at 11:50:59PM +0200, Thorsten Kukuk wrote:
> > > >
> > > > Hi,
> > > >
> > > > I got the following test program. I know, it is very ugly and there
> > > > are a lot of things somebody should not do, but this is something
> > > > what programs like sshd are doing.
> > >
> > > Then they should be fixed.  Neither syslog, nor printf, nor fflush
> > > are supposed to be async-signal safe, nor they actually are in glibc.
> >
> > Yes, but the problem is: Nearly every daemon on a Linux system is
> > calling syslog() in a signal handler and it seems to be very easy
> > to deadlock them on every Linux system running glibc/NPTL. While
> > there seems to be no other system with the same problem.
> >
> 
> Then what has change from glibc-2.3.3 (RHEL 3) until now? Because I have
> not seen this problem before.

The test case also deadlocks on a RHEL 3 machine very fast.

> I have reviewed all the changes to
> lowlevellock.h since and I do not see any change that would effect this. In
> fact your test case should show that same hang there.

The difference is: glibc with linuxthreads compiled only uses the
locking, if the program is linked against pthread.

glibc with NPTL compiled always uses locking (__libc_lock_lock always
calls lll_lock).

Uli, Jakub, is this really necessary? Wouldn't it be better to add the
one extra compare?

> Have the daemon's changed recently to add the syslog() call to the signal
> handler?

No, this is very, very old.

  Thorsten

-- 
Thorsten Kukuk       http://www.suse.de/~kukuk/        kukuk@suse.de
SuSE Linux AG        Maxfeldstr. 5                 D-90409 Nuernberg
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