Re: knlist_empty locking fix

On Friday, January 27, 2012 12:52:18 pm Kostik Belousov wrote:
> On Fri, Jan 27, 2012 at 09:42:58AM -0800, Doug Ambrisko wrote:
> > Andrew Boyer writes:
> > | On Jan 27, 2012, at 12:15 PM, Doug Ambrisko wrote:
> > | 
> > | > John Baldwin writes:
> > | > | Agreed, I think the missing locking should just be added to the aio 
code.
> > | > 
> > | > Okay so then just:
> > | > 
> > | > Index: vfs_aio.c
> > | > ===================================================================
> > | > RCS file: /usr/local/cvsroot/freebsd/src/sys/kern/vfs_aio.c,v
> > | > retrieving revision 1.243.2.3.4.1
> > | > diff -u -p -r1.243.2.3.4.1 vfs_aio.c
> > | > --- vfs_aio.c	21 Dec 2010 17:09:25 -0000	1.243.2.3.4.1
> > | > +++ vfs_aio.c	27 Jan 2012 17:07:11 -0000
> > | > _at__at_ -2509,9 +2509,12 _at__at_ static void
> > | > filt_aiodetach(struct knote *kn)
> > | > {
> > | > 	struct aiocblist *aiocbe = kn->kn_ptr.p_aio;
> > | > +	struct knlist *knl = &aiocbe->klist;
> > | > 
> > | > -	if (!knlist_empty(&aiocbe->klist))
> > | > -		knlist_remove(&aiocbe->klist, kn, 0);
> > | > +	knl->kl_lock(knl->kl_lockarg);
> > | > +	if (!knlist_empty(knl))
> > | > +		knlist_remove(knl, kn, 1);
> > | > +	knl->kl_unlock(knl->kl_lockarg);
> > | > }
> > | > 
> > | > /* kqueue filter function */
> > | > 
> > | > I was trying to be consistant with knlist_remove but this is a much
> > | > smaller change that can be merge to older branches.
> > |  
> > | Does filt_liodetach() need the same treatment?
> > 
> > Yes, I had that in the original.  I updated that and optimized
> > the knl to just get the structure needed.
> > 
> > Index: vfs_aio.c
> > ===================================================================
> > RCS file: /usr/local/cvsroot/freebsd/src/sys/kern/vfs_aio.c,v
> > retrieving revision 1.243.2.3.4.1
> > diff -u -p -r1.243.2.3.4.1 vfs_aio.c
> > --- vfs_aio.c	21 Dec 2010 17:09:25 -0000	1.243.2.3.4.1
> > +++ vfs_aio.c	27 Jan 2012 17:35:47 -0000
> > _at__at_ -2508,10 +2508,12 _at__at_ filt_aioattach(struct knote *kn)
> >  static void
> >  filt_aiodetach(struct knote *kn)
> >  {
> > -	struct aiocblist *aiocbe = kn->kn_ptr.p_aio;
> > +	struct knlist *knl = &kn->kn_ptr.p_aio->klist;
> >  
> > -	if (!knlist_empty(&aiocbe->klist))
> > -		knlist_remove(&aiocbe->klist, kn, 0);
> > +	knl->kl_lock(knl->kl_lockarg);
> > +	if (!knlist_empty(knl))
> > +		knlist_remove(knl, kn, 1);
> > +	knl->kl_unlock(knl->kl_lockarg);
> >  }
> >  
> >  /* kqueue filter function */
> > _at__at_ -2553,10 +2555,12 _at__at_ filt_lioattach(struct knote *kn)
> >  static void
> >  filt_liodetach(struct knote *kn)
> >  {
> > -	struct aioliojob * lj = kn->kn_ptr.p_lio;
> > +	struct knlist *knl = &kn->kn_ptr.p_lio->klist;
> It is easy to be style-compiant there and move initialization of knl
> after the blank line.
> 
> Do you need two different functions now ? I think you can leave just one.

Hmm, I think p_lio != p_aio, so two functions are required.

I think the patch looks fine.  The style fix to not assign 'knl' in its
declaration would be nice to fix as you suggested, but that's minor.

-- 
John Baldwin