Re: [PATCH 1/2] fs/ocfs2/dlm: Eliminate update of list_for_each_entry loop cursor

[Sunil Mushran <sunil.mushran@xxxxxxxxxx>]

I think it got lost in the shuffle. We had decided to use the list_for_each().
The code is simpler to understand than the other proposed fix.

Joel, do you want me to send a patch?

On 11/02/2011 12:39 AM, Dan Carpenter wrote:
> What ever happened with this?  The bug is still there in the latest
> kernel.
>
> I think from previous discussion about this that we only ever have
> one lock so lock->ml.cookie is always equal to ml->cookie and we
> never set lock to NULL.  So we never actually hit the NULL deref.
> But it should probably still be cleaned up.
>
> regards,
> dan carpenter
>
> On Wed, Aug 11, 2010 at 05:03:56PM -0700, Joel Becker wrote:
> > On Sat, Aug 07, 2010 at 11:09:13AM +0200, Julia Lawall wrote:
> > > From: Julia Lawall<julia@xxxxxxx>
> > >
> > > list_for_each_entry uses its first argument to move from one element to the
> > > next, so modifying it can break the iteration.
> > 	Thanks for catching the bug.  It was introduced by 800deef3
> > [ocfs2: use list_for_each_entry where benefical].  I blame Christoph.
> >
> > > diff --git a/fs/ocfs2/dlm/dlmrecovery.c b/fs/ocfs2/dlm/dlmrecovery.c
> > > index 9dfaac7..7084a11 100644
> > > --- a/fs/ocfs2/dlm/dlmrecovery.c
> > > +++ b/fs/ocfs2/dlm/dlmrecovery.c
> > > @@ -1792,10 +1792,10 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
> > >   			for (j = DLM_GRANTED_LIST; j<= DLM_BLOCKED_LIST; j++) {
> > >   				tmpq = dlm_list_idx_to_ptr(res, j);
> > >   				list_for_each_entry(lock, tmpq, list) {
> > > -					if (lock->ml.cookie != ml->cookie)
> > > +					if (lock->ml.cookie != ml->cookie) {
> > >   						lock = NULL;
> > > -					else
> > >   						break;
> > > +					}
> > >   				}
> > >   				if (lock)
> > >   					break;
> > 	However, this is not the correct solution.  The goal of the
> > original code, which used to use list_for_each(), was to leave lock
> > non-NULL if the cookie was found.  Your version merely exits the loop on
> > the first non-matching entry, always leaving lock==NULL if there is a
> > non-matching entry.
> > 	One possible solution is to return the original code:
> >
> > --8<-----------------------------------------------------------------
> > @@ -1747,7 +1747,7 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
> >   				     struct dlm_migratable_lockres *mres)
> >   {
> >   	struct dlm_migratable_lock *ml;
> > -	struct list_head *queue;
> > +	struct list_head *queue, *iter;
> >   	struct list_head *tmpq = NULL;
> >   	struct dlm_lock *newlock = NULL;
> >   	struct dlm_lockstatus *lksb = NULL;
> > @@ -1791,11 +1791,12 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
> >   			spin_lock(&res->spinlock);
> >   			for (j = DLM_GRANTED_LIST; j<= DLM_BLOCKED_LIST; j++) {
> >   				tmpq = dlm_list_idx_to_ptr(res, j);
> > -				list_for_each_entry(lock, tmpq, list) {
> > -					if (lock->ml.cookie != ml->cookie)
> > -						lock = NULL;
> > -					else
> > +				list_for_each(iter, tmpq) {
> > +					lock = list_entry(iter, struct dlm_lock, list);
> > +
> > +					if (lock->ml.cookie == ml->cookie)
> >   						break;
> > +					lock = NULL;
> >   				}
> >   				if (lock)
> >   					break;
> > -->8-----------------------------------------------------------------
> >
> > 	Another approach would be to keep list_for_each_entry() around,
> > but use a better check for entry existence:
> >
> > --8<-----------------------------------------------------------------
> > @@ -1792,13 +1792,12 @@ static int dlm_process_recovery_data(struct dlm_ctxt *dlm,
> >   			for (j = DLM_GRANTED_LIST; j<= DLM_BLOCKED_LIST; j++) {
> >   				tmpq = dlm_list_idx_to_ptr(res, j);
> >   				list_for_each_entry(lock, tmpq, list) {
> > -					if (lock->ml.cookie != ml->cookie)
> > -						lock = NULL;
> > -					else
> > +					if (lock->ml.cookie == ml->cookie)
> >   						break;
> >   				}
> > -				if (lock)
> > +				if (&lock->list != tmpq)
> >   					break;
> > +				lock = NULL;
> >   			}
> >
> >   			/* lock is always created locally first, and
> > -->8-----------------------------------------------------------------
> >
> > 	I think I like the second one better.  Sunil, what do you think?
> >
> > Joel
> >
> > --
> >
> > Life's Little Instruction Book #335
> >
> > 	"Every so often, push your luck."
> >
> > Joel Becker
> > Consulting Software Developer
> > Oracle
> > E-mail: joel.becker@xxxxxxxxxx
> > Phone: (650) 506-8127
> > --
> > To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in
> > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html