svn commit: r218967 - head/sys/kern

Alexander Best arundel at freebsd.org
Wed Feb 23 14:30:13 UTC 2011


On Wed Feb 23 11, Kostik Belousov wrote:
> On Wed, Feb 23, 2011 at 01:57:34PM +0000, Alexander Best wrote:
> > On Wed Feb 23 11, Kostik Belousov wrote:
> > > On Wed, Feb 23, 2011 at 12:56:25PM +0000, John Baldwin wrote:
> > > > Author: jhb
> > > > Date: Wed Feb 23 12:56:25 2011
> > > > New Revision: 218967
> > > > URL: http://svn.freebsd.org/changeset/base/218967
> > > > 
> > > > Log:
> > > >   Fix off-by-one error in check against max_threads_per_proc.
> > > >   
> > > >   Submitted by:	arundel
> > > >   MFC after:	1 week
> > > > 
> > > > Modified:
> > > >   head/sys/kern/kern_thr.c
> > > > 
> > > > Modified: head/sys/kern/kern_thr.c
> > > > ==============================================================================
> > > > --- head/sys/kern/kern_thr.c	Wed Feb 23 10:28:37 2011	(r218966)
> > > > +++ head/sys/kern/kern_thr.c	Wed Feb 23 12:56:25 2011	(r218967)
> > > > @@ -153,7 +153,7 @@ create_thread(struct thread *td, mcontex
> > > >  	p = td->td_proc;
> > > >  
> > > >  	/* Have race condition but it is cheap. */
> > > > -	if (p->p_numthreads >= max_threads_per_proc) {
> > > > +	if (p->p_numthreads > max_threads_per_proc) {
> > > >  		++max_threads_hits;
> > > >  		return (EPROCLIM);
> > > >  	}
> > > 
> > > I do not think there was off by one error. The create_thread() function
> > > is called to create new thread, and before the process thread counter
> > > is incremented in thread_link(). The old test tried to not allow more
> > > then max_threads_per_proc threads in a process, now it allows to
> > > create max_threads_per_proc.
> > 
> > doesn't the semantics of the term "maximum" imply that it's own value is also
> > valid?
> > 
> > if a sign says maximum weight 2000kg, does that mean that a weight of 2000kg is
> > invalid and the highest valid weight is 1999,999..kg?
> > 
> > cheers.
> > alex
> > 
> > > 
> > > My guess is that the reference to mentioned pthread_vfork_test failed
> > > because reporter set kern.threads.max_threads_per_proc to 100. The
> > > test actually tries to create 101 threads, 1 main + 100 new.
> > 
> > so the main process counts as 1 thread and for each pthread_create
> > invokation the thread number gets bumped up?
> >
> > so with a process doing a single pthread_create() that would imply
> > this process is having a thread count of 2?
> 
> Exactly. The main thread is the same as all others (almost).

thanks for the hint. i wasn't aware of that. however now proctsta -akk also
displaying a thread id for a process with no additional threads makes a lot
more sense. ;)

so in theory:
kern.threads.max_threads_per_proc=0 and kern.threads.max_threads_per_proc=1
both forbid a process to trigger any new threads.

cheers.
alex

-- 
a13x


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