Re: knlist_empty locking fix

John Baldwin writes:
| 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.

Correct, even thought they are together in a union, the structures are
different so klist would have a different offset for each function.
 
| 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.

Here is the updated version that seems to work fine.

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 18:22:10 -0000
_at__at_ -2508,10 +2508,13 _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;
 
-	if (!knlist_empty(&aiocbe->klist))
-		knlist_remove(&aiocbe->klist, kn, 0);
+	knl = &kn->kn_ptr.p_aio->klist;
+	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 +2556,13 _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;
 
-	if (!knlist_empty(&lj->klist))
-		knlist_remove(&lj->klist, kn, 0);
+	knl = &kn->kn_ptr.p_lio->klist;
+	knl->kl_lock(knl->kl_lockarg);
+	if (!knlist_empty(knl))
+		knlist_remove(knl, kn, 1);
+	knl->kl_unlock(knl->kl_lockarg);
 }
 
 /* kqueue filter function */

Thanks,

Doug A.