First, vehement apologies for sending an RFC patch against such an old
kernel. This is (potentially) a bug fix for a crash that we've been seeing
in 3.2 and 3.10, and, AFAICT, the underlying issue has not been addressed.
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"
#0 [ffff8820ceec1450] machine_kexec at ffffffff81036865
#1 [ffff8820ceec14a0] crash_kexec at ffffffff810aa3e8
#2 [ffff8820ceec1570] oops_end at ffffffff8160b458
#3 [ffff8820ceec15a0] no_context at ffffffff816000e2
#4 [ffff8820ceec1600] __bad_area_nosemaphore at ffffffff816002c7
#5 [ffff8820ceec1650] bad_area at ffffffff81600515
#6 [ffff8820ceec1680] __do_page_fault at ffffffff8160df9e
#7 [ffff8820ceec1790] do_page_fault at ffffffff8160e09e
#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 [ffff8820ceec1870] qdisc_tree_decrease_qlen at ffffffff81565375
#10 [ffff8820ceec18a0] fq_codel_dequeue at ffffffffa084e0a0 [sch_fq_codel]
#11 [ffff8820ceec1940] fq_codel_reset at ffffffffa084e2f8 [sch_fq_codel]
#12 [ffff8820ceec1960] qdisc_destroy at ffffffff81560d2d
#13 [ffff8820ceec1980] htb_destroy_class at ffffffffa08408f8 [sch_htb]
#14 [ffff8820ceec19a0] htb_put at ffffffffa084095c [sch_htb]
#15 [ffff8820ceec19b0] tc_ctl_tclass at ffffffff815645a3
#16 [ffff8820ceec1a60] rtnetlink_rcv_msg at ffffffff81552cb0
#17 [ffff8820ceec1ae0] netlink_rcv_skb at ffffffff8156cfd1
#18 [ffff8820ceec1b10] rtnetlink_rcv at ffffffff8154f7f5
#19 [ffff8820ceec1b30] netlink_unicast at ffffffff8156c929
#20 [ffff8820ceec1b80] netlink_sendmsg at ffffffff8156cc69
#21 [ffff8820ceec1c10] sock_sendmsg at ffffffff81528cf6
#22 [ffff8820ceec1d60] ___sys_sendmsg at ffffffff815290bc
#23 [ffff8820ceec1f00] __sys_sendmsg at ffffffff8152c589
#24 [ffff8820ceec1f70] sys_sendmsg at ffffffff8152c5e2
#25 [ffff8820ceec1f80] system_call_fastpath at ffffffff816128c2
RIP: 00007f31695448b0 RSP: 00007fffb1509538 RFLAGS: 00010293
RAX: 000000000000002e RBX: ffffffff816128c2 RCX: 0000000000000030
RDX: 0000000000000000 RSI: 00007fffb15054d0 RDI: 0000000000000005
RBP: 00007fffb150a5f0 R8: 0000000000000007 R9: 0000000000000000
R10: 00007fffb1505230 R11: 0000000000000246 R12: ffffffff8152c5e2
R13: ffff8820ceec1f78 R14: 0000000000642760 R15: 00007fffb15095b0
ORIG_RAX: 000000000000002e CS: 0033 SS: 002b
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 2d2f079..f5d48dd 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -700,8 +700,15 @@ 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;
}
--
Alex Gartrell <agartr...@fb.com>
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