We have an application that invokes tc to delete the root every time the
config changes. As a result we stress the cleanup code and were seeing the
following panic:
crash> bt
PID: 630839 TASK: ffff8823c990d280 CPU: 14 COMMAND: "tc"
[... snip ...]
#8 [ffff8820ceec17a0] page_fault at ffffffff8160a8c2
[exception RIP: htb_qlen_notify+24]
RIP: ffffffffa0841718 RSP: ffff8820ceec1858 RFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88241747b400
RDX: ffff88241747b408 RSI: 0000000000000000 RDI: ffff8811fb27d000
RBP: ffff8820ceec1868 R8: ffff88120cdeff24 R9: ffff88120cdeff30
R10: 0000000000000bd4 R11: ffffffffa0840919 R12: ffffffffa0843340
R13: 0000000000000000 R14: 0000000000000001 R15: ffff8808dae5c2e8
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#9 [...] qdisc_tree_decrease_qlen at ffffffff81565375
#10 [...] fq_codel_dequeue at ffffffffa084e0a0 [sch_fq_codel]
#11 [...] fq_codel_reset at ffffffffa084e2f8 [sch_fq_codel]
#12 [...] qdisc_destroy at ffffffff81560d2d
#13 [...] htb_destroy_class at ffffffffa08408f8 [sch_htb]
#14 [...] htb_put at ffffffffa084095c [sch_htb]
#15 [...] tc_ctl_tclass at ffffffff815645a3
#16 [...] rtnetlink_rcv_msg at ffffffff81552cb0
[... snip ...]
To my understanding, the following situation is taking place.
tc_ctl_tclass
-> htb_delete
-> class is deleted from clhash
-> htb_put
-> qdisc_destroy
-> fq_codel_reset
-> fq_codel_dequeue
-> qdidsc_tree_decrease_qlen
-> cl = htb_get # returns NULL, removed in htb_delete
-> htb_qlen_notify(sch, NULL) # BOOM
This patch checks cl for 0 before invoking qlen_notify and put. The notify
is not necessary in this case, as the parent has already been deactivated
anyway.
Signed-off-by: Alex Gartrell <agartr...@fb.com>
---
net/sched/sch_api.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index f06aa01..46be5e5 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -762,8 +762,15 @@ void qdisc_tree_decrease_qlen(struct Qdisc *sch, unsigned
int n)
cops = sch->ops->cl_ops;
if (cops->qlen_notify) {
cl = cops->get(sch, parentid);
- cops->qlen_notify(sch, cl);
- cops->put(sch, cl);
+ /* This will be 0 in the event that cl is being
+ * destroyed, in which case we should not attempt
+ * to invoke qlen_notify upon it (it must be
+ * cleaned up otherwise anyway.
+ */
+ if (cl != 0) {
+ cops->qlen_notify(sch, cl);
+ cops->put(sch, cl);
+ }
}
sch->q.qlen -= n;
__qdisc_qstats_drop(sch, drops);
--
Alex Gartrell <agartr...@fb.com>
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