On 07/20/15 15:40, Alex Gartrell wrote:
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
=========> this part looks suspicious. Why is reset invoking
a dequeue? Shouldnt a destroy just purge the queue?
-> fq_codel_dequeue
-> qdidsc_tree_decrease_qlen
-> cl = htb_get # returns NULL, removed in htb_delete
-> htb_qlen_notify(sch, NULL) # BOOM
It is worrisome to fix the core code for this. The root cause seems to
be codel. Dont have time but in general, reset would be something like:
struct fq_codel_sched_data *q = qdisc_priv(sch);
qdisc_reset(q)
or something along those lines...
But certainly dequeue semantics dont seem right there..
cheers,
jamal
cheers,
jamal
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