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pkt_sched: Change misleading code in class delete. 

While looking for a possible reason of bugzilla report on HTB oops:
http://bugzilla.kernel.org/show_bug.cgi?id=12858
I found the code in htb_delete calling htb_destroy_class on zero
refcount is very misleading: it can suggest this is a common path, and
destroy is called under sch_tree_lock. Actually, this can never happen
like this because before deletion cops->get() is done, and after
delete a class is still used by tclass_notify. The class destroy is
always called from cops->put(), so without sch_tree_lock.

This doesn't mean much now (since 2.6.27) because all vulnerable calls
were moved from htb_destroy_class to htb_delete, but there was a bug
in older kernels. The same change is done for other classful scheds,
which, it seems, didn't have similar locking problems here.

Reported-by: m0sia <m0sia@m0sia.ru>
Signed-off-by: Jarek Poplawski <jarkao2@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jarek Poplawski 2009-03-15 20:00:19 -07:00 committed by David S. Miller
parent 8bdd663aba
commit 7cd0a63872
4 changed files with 20 additions and 8 deletions
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7
net/sched/sch_cbq.c
View File

@ -1960,8 +1960,11 @@ static int cbq_delete(struct Qdisc *sch, unsigned long arg)
cbq_rmprio(q, cl);
sch_tree_unlock(sch);
if (--cl->refcnt == 0)
cbq_destroy_class(sch, cl);
BUG_ON(--cl->refcnt == 0);
/*
* This shouldn't happen: we "hold" one cops->get() when called
* from tc_ctl_tclass; the destroy method is done from cops->put().
*/
return 0;
}

7
net/sched/sch_drr.c
View File

@ -155,8 +155,11 @@ static int drr_delete_class(struct Qdisc *sch, unsigned long arg)
drr_purge_queue(cl);
qdisc_class_hash_remove(&q->clhash, &cl->common);
if (--cl->refcnt == 0)
drr_destroy_class(sch, cl);
BUG_ON(--cl->refcnt == 0);
/*
* This shouldn't happen: we "hold" one cops->get() when called
* from tc_ctl_tclass; the destroy method is done from cops->put().
*/
sch_tree_unlock(sch);
return 0;

7
net/sched/sch_hfsc.c
View File

@ -1139,8 +1139,11 @@ hfsc_delete_class(struct Qdisc *sch, unsigned long arg)
hfsc_purge_queue(sch, cl);
qdisc_class_hash_remove(&q->clhash, &cl->cl_common);
if (--cl->refcnt == 0)
hfsc_destroy_class(sch, cl);
BUG_ON(--cl->refcnt == 0);
/*
* This shouldn't happen: we "hold" one cops->get() when called
* from tc_ctl_tclass; the destroy method is done from cops->put().
*/
sch_tree_unlock(sch);
return 0;

7
net/sched/sch_htb.c
View File

@ -1275,8 +1275,11 @@ static int htb_delete(struct Qdisc *sch, unsigned long arg)
if (last_child)
htb_parent_to_leaf(q, cl, new_q);
if (--cl->refcnt == 0)
htb_destroy_class(sch, cl);
BUG_ON(--cl->refcnt == 0);
/*
* This shouldn't happen: we "hold" one cops->get() when called
* from tc_ctl_tclass; the destroy method is done from cops->put().
*/
sch_tree_unlock(sch);
return 0;