[PATCH AUTOSEL 5.3 26/33] net: sched: multiq: don't call qdisc_put() while holding tree lock

Sasha Levin
2019-10-25T14:05:42Z

From: Vlad Buslov <vladbu@mellanox.com>

[ Upstream commit c2999f7fb05b87da4060e38150c70fa46794d82b ]

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 multiq:

tc qdisc add dev ens1f0 root handle 1: multiq
tc qdisc add dev ens1f0 parent 1:10 handle 50: sfq perturb 10
ethtool -L ens1f0 combined 2
tc qdisc change dev ens1f0 root handle 1: multiq

Resulting dmesg:

[ 5539.419344] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:909
[ 5539.420945] in_atomic(): 1, irqs_disabled(): 0, pid: 27658, name: tc
[ 5539.422435] INFO: lockdep is turned off.
[ 5539.423904] CPU: 21 PID: 27658 Comm: tc Tainted: G W 5.3.0-rc8+ #721
[ 5539.425400] Hardware name: Supermicro SYS-2028TP-DECR/X10DRT-P, BIOS 2.0b 03/30/2017
[ 5539.426911] Call Trace:
[ 5539.428380] dump_stack+0x85/0xc0
[ 5539.429823] ___might_sleep.cold+0xac/0xbc
[ 5539.431262] __mutex_lock+0x5b/0x960
[ 5539.432682] ? tcf_chain0_head_change_cb_del.isra.0+0x1b/0xf0
[ 5539.434103] ? __nla_validate_parse+0x51/0x840
[ 5539.435493] ? tcf_chain0_head_change_cb_del.isra.0+0x1b/0xf0
[ 5539.436903] tcf_chain0_head_change_cb_del.isra.0+0x1b/0xf0
[ 5539.438327] tcf_block_put_ext.part.0+0x21/0x50
[ 5539.439752] tcf_block_put+0x50/0x70
[ 5539.441165] sfq_destroy+0x15/0x50 [sch_sfq]
[ 5539.442570] qdisc_destroy+0x5f/0x160
[ 5539.444000] multiq_tune+0x14a/0x420 [sch_multiq]
[ 5539.445421] tc_modify_qdisc+0x324/0x840
[ 5539.446841] rtnetlink_rcv_msg+0x170/0x4b0
[ 5539.448269] ? netlink_deliver_tap+0x95/0x400
[ 5539.449691] ? rtnl_dellink+0x2d0/0x2d0
[ 5539.451116] netlink_rcv_skb+0x49/0x110
[ 5539.452522] netlink_unicast+0x171/0x200
[ 5539.453914] netlink_sendmsg+0x224/0x3f0
[ 5539.455304] sock_sendmsg+0x5e/0x60
[ 5539.456686] ___sys_sendmsg+0x2ae/0x330
[ 5539.458071] ? ___sys_recvmsg+0x159/0x1f0
[ 5539.459461] ? do_wp_page+0x9c/0x790
[ 5539.460846] ? __handle_mm_fault+0xcd3/0x19e0
[ 5539.462263] __sys_sendmsg+0x59/0xa0
[ 5539.463661] do_syscall_64+0x5c/0xb0
[ 5539.465044] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 5539.466454] RIP: 0033:0x7f1fe08177b8
[ 5539.467863] 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
[ 5539.470906] RSP: 002b:00007ffe812de5d8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
[ 5539.472483] RAX: ffffffffffffffda RBX: 000000005d8135e3 RCX: 00007f1fe08177b8
[ 5539.474069] RDX: 0000000000000000 RSI: 00007ffe812de640 RDI: 0000000000000003
[ 5539.475655] RBP: 0000000000000000 R08: 0000000000000001 R09: 000000000182e9b0
[ 5539.477203] R10: 0000000000404eda R11: 0000000000000246 R12: 0000000000000001
[ 5539.478699] R13: 000000000047f640 R14: 0000000000000000 R15: 0000000000000000

Rearrange locking in multiq_tune() in following ways:

- In loop that removes Qdiscs from disabled queues, call
qdisc_purge_queue() instead of qdisc_tree_flush_backlog() on Qdisc that
is being destroyed. Save the Qdisc in temporary allocated array and call
qdisc_put() on each element of the array after sch tree lock is released.
This is safe to do because Qdiscs have already been reset by
qdisc_purge_queue() inside sch tree lock critical section.

- Do the same change for second loop that initializes Qdiscs for newly
enabled queues in multiq_tune() function. Since sch tree lock is obtained
and released on each iteration of this loop, just call qdisc_put()
directly outside of critical section. Don't verify that old Qdisc is not
noop_qdisc before releasing reference to it because such check is already
performed by qdisc_put*() functions.

Fixes: c266f64dbfa2 ("net: sched: protect block state with mutex")
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/sch_multiq.c | 23 ++++++++++++++++-------
1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/net/sched/sch_multiq.c b/net/sched/sch_multiq.c
index e1087746f6a29..b2b7fdb06fc62 100644
--- a/net/sched/sch_multiq.c
+++ b/net/sched/sch_multiq.c
@@ -174,7 +174,8 @@ static int multiq_tune(struct Qdisc *sch, struct nlattr *opt,
{
struct multiq_sched_data *q = qdisc_priv(sch);
struct tc_multiq_qopt *qopt;
- int i;
+ struct Qdisc **removed;
+ int i, n_removed = 0;

if (!netif_is_multiqueue(qdisc_dev(sch)))
return -EOPNOTSUPP;
@@ -185,6 +186,11 @@ static int multiq_tune(struct Qdisc *sch, struct nlattr *opt,

qopt->bands = qdisc_dev(sch)->real_num_tx_queues;

+ removed = kmalloc(sizeof(*removed) * (q->max_bands - q->bands),
+ GFP_KERNEL);
+ if (!removed)
+ return -ENOMEM;
+
sch_tree_lock(sch);
q->bands = qopt->bands;
for (i = q->bands; i < q->max_bands; i++) {
@@ -192,13 +198,17 @@ static int multiq_tune(struct Qdisc *sch, struct nlattr *opt,
struct Qdisc *child = q->queues[i];

q->queues[i] = &noop_qdisc;
- qdisc_tree_flush_backlog(child);
- qdisc_put(child);
+ qdisc_purge_queue(child);
+ removed[n_removed++] = child;
}
}

sch_tree_unlock(sch);

+ for (i = 0; i < n_removed; i++)
+ qdisc_put(removed[i]);
+ kfree(removed);
+
for (i = 0; i < q->bands; i++) {
if (q->queues[i] == &noop_qdisc) {
struct Qdisc *child, *old;
@@ -213,11 +223,10 @@ static int multiq_tune(struct Qdisc *sch, struct nlattr *opt,
if (child != &noop_qdisc)
qdisc_hash_add(child, true);

- if (old != &noop_qdisc) {
- qdisc_tree_flush_backlog(old);
- qdisc_put(old);
- }
+ if (old != &noop_qdisc)
+ qdisc_purge_queue(old);
sch_tree_unlock(sch);
+ qdisc_put(old);
}
}
}
--
2.20.1