[PATCH net 1/3] net: sched: sch_htb: don't call qdisc_put() while holding tree lock

[Vlad Buslov <vladbu@mellanox.com>]

Recent changes that removed rtnl dependency from rules update path of tc
also made tcf_block_put() function sleeping. This function is called from
ops->destroy() of several Qdisc implementations, which in turn is called by
qdisc_put(). Some Qdiscs call qdisc_put() while holding sch tree spinlock,
which results sleeping-while-atomic BUG.

Steps to reproduce for htb:

tc qdisc add dev ens1f0 root handle 1: htb default 12
tc class add dev ens1f0 parent 1: classid 1:1 htb rate 100kbps ceil 100kbps
tc qdisc add dev ens1f0 parent 1:1 handle 40: sfq perturb 10
tc class add dev ens1f0 parent 1:1 classid 1:2 htb rate 100kbps ceil 100kbps

Resulting dmesg:

[ 4791.148551] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:909
[ 4791.151354] in_atomic(): 1, irqs_disabled(): 0, pid: 27273, name: tc
[ 4791.152805] INFO: lockdep is turned off.
[ 4791.153605] CPU: 19 PID: 27273 Comm: tc Tainted: G        W         5.3.0-rc8+ #721
[ 4791.154336] Hardware name: Supermicro SYS-2028TP-DECR/X10DRT-P, BIOS 2.0b 03/30/2017
[ 4791.155075] Call Trace:
[ 4791.155803]  dump_stack+0x85/0xc0
[ 4791.156529]  ___might_sleep.cold+0xac/0xbc
[ 4791.157251]  __mutex_lock+0x5b/0x960
[ 4791.157966]  ? console_unlock+0x363/0x5d0
[ 4791.158676]  ? tcf_chain0_head_change_cb_del.isra.0+0x1b/0xf0
[ 4791.159395]  ? tcf_chain0_head_change_cb_del.isra.0+0x1b/0xf0
[ 4791.160103]  tcf_chain0_head_change_cb_del.isra.0+0x1b/0xf0
[ 4791.160815]  tcf_block_put_ext.part.0+0x21/0x50
[ 4791.161530]  tcf_block_put+0x50/0x70
[ 4791.162233]  sfq_destroy+0x15/0x50 [sch_sfq]
[ 4791.162936]  qdisc_destroy+0x5f/0x160
[ 4791.163642]  htb_change_class.cold+0x5df/0x69d [sch_htb]
[ 4791.164505]  tc_ctl_tclass+0x19d/0x480
[ 4791.165360]  rtnetlink_rcv_msg+0x170/0x4b0
[ 4791.166191]  ? netlink_deliver_tap+0x95/0x400
[ 4791.166907]  ? rtnl_dellink+0x2d0/0x2d0
[ 4791.167625]  netlink_rcv_skb+0x49/0x110
[ 4791.168345]  netlink_unicast+0x171/0x200
[ 4791.169058]  netlink_sendmsg+0x224/0x3f0
[ 4791.169771]  sock_sendmsg+0x5e/0x60
[ 4791.170475]  ___sys_sendmsg+0x2ae/0x330
[ 4791.171183]  ? ___sys_recvmsg+0x159/0x1f0
[ 4791.171894]  ? do_wp_page+0x9c/0x790
[ 4791.172595]  ? __handle_mm_fault+0xcd3/0x19e0
[ 4791.173309]  __sys_sendmsg+0x59/0xa0
[ 4791.174024]  do_syscall_64+0x5c/0xb0
[ 4791.174725]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 4791.175435] RIP: 0033:0x7f0aa41497b8
[ 4791.176129] Code: 89 02 48 c7 c0 ff ff ff ff eb bb 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 8d 05 65 8f 0c 00 8b 00 85 c0 75 17 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 58 c3 0f 1f 80 00 00 00 00 48 83 ec 28 89 5
4
[ 4791.177532] RSP: 002b:00007fff4e37d588 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
[ 4791.178243] RAX: ffffffffffffffda RBX: 000000005d8132f7 RCX: 00007f0aa41497b8
[ 4791.178947] RDX: 0000000000000000 RSI: 00007fff4e37d5f0 RDI: 0000000000000003
[ 4791.179662] RBP: 0000000000000000 R08: 0000000000000001 R09: 00000000020149a0
[ 4791.180382] R10: 0000000000404eda R11: 0000000000000246 R12: 0000000000000001
[ 4791.181100] R13: 000000000047f640 R14: 0000000000000000 R15: 0000000000000000

Fix the issue by saving parent->leaf.q to local temporary variable and
calling qdisc_put() with it after sch tree lock is released.

Fixes: c266f64dbfa2 ("net: sched: protect block state with mutex")
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
---
 net/sched/sch_htb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 7bcf20ef9145..8184c87da8be 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1302,6 +1302,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 	struct htb_class *cl = (struct htb_class *)*arg, *parent;
 	struct nlattr *opt = tca[TCA_OPTIONS];
 	struct nlattr *tb[TCA_HTB_MAX + 1];
+	struct Qdisc *parent_qdisc = NULL;
 	struct tc_htb_opt *hopt;
 	u64 rate64, ceil64;
 	int warn = 0;
@@ -1401,7 +1402,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 		if (parent && !parent->level) {
 			/* turn parent into inner node */
 			qdisc_purge_queue(parent->leaf.q);
-			qdisc_put(parent->leaf.q);
+			parent_qdisc = parent->leaf.q;
 			if (parent->prio_activity)
 				htb_deactivate(q, parent);
 
@@ -1480,6 +1481,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 	cl->cbuffer = PSCHED_TICKS2NS(hopt->cbuffer);
 
 	sch_tree_unlock(sch);
+	qdisc_put(parent_qdisc);
 
 	if (warn)
 		pr_warn("HTB: quantum of class %X is %s. Consider r2q change.\n",
-- 
2.21.0