On Fri, May 17, 2002 at 23:02:55 -0700, Alfred Perlstein wrote:
> * Kenneth D. Merry <[EMAIL PROTECTED]> [020517 22:40] wrote:
> > 
> > I have released a new set of zero copy sockets patches, against -current
> > from today (May 17th, 2002).
> > 
> > The main change is to deal with the vfs_ioopt changes that Alan Cox made in
> > kern_subr.c.  (They conflicted a bit with the zero copy receive code.)
> > 
> > The patches and the FAQ are available here:
> > 
> > http://people.freebsd.org/~ken/zero_copy/
> > 
> > Comments, questions and reviews are all welcome!
> jumbo_vm_init() has a bunch of bugs
> first it doesn't work right if called concurrently.
> you need to protect the initialization of jumbo_vm_object otherwise
> bad things can happen.  my suggestion is to store the results of
> vm_object_allocate into a temporary, grab the mutex and then check
> to see if jumbo_vm_object has been initialized again if it has then
> free the object, otherwise store the allocated object into the
> global and continue.

The problem here is that the mutex needs to be initialized before I can
acquire it, and there's going to be a race between checking to see
whether it has been initialized and actually initializing it.


        if (!mtx_initialized(&jumbo_mutex))
                mtx_init(&jumbo_mutex, "jumbo mutex", NULL, MTX_DEF);


        if (jumbo_vm_object != NULL) {
                return (1);

        /* allocate our object */
        jumbo_vm_object = vm_object_allocate(OBJT_DEFAULT, JUMBO_MAX_PAGES);

The above would work, I think, if it weren't for the race in the mutex
initialization, and assuming I can allocate a vm object while holding
the jumbo mutex.


> you may not call malloc(9) with M_WAITOK while holding a mutex.

Ahh, okay.

> entry = jumbo_kmap_inuse.slh_first;
> I'm sure that should use a list macro.

Yes, SLIST_FIRST(), thanks.

> That's all I see off the bat. :)  Looks cool though.

Cool, thanks for the feedback!

Kenneth Merry

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