When the following snippet is run, lockdep will report a deadlock[1].
/* Acquire all queues dim_locks */
for (i = 0; i < vi->max_queue_pairs; i++)
mutex_lock(&vi->rq[i].dim_lock);
There's no deadlock here because the vq locks are always taken
in the same order, but lockdep can not figure it out. So refactoring
the code to alleviate the problem.
[1]
========================================================
WARNING: possible recursive locking detected
6.9.0-rc7+ #319 Not tainted
--------------------------------------------
ethtool/962 is trying to acquire lock:
but task is already holding lock:
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&vi->rq[i].dim_lock);
lock(&vi->rq[i].dim_lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
3 locks held by ethtool/962:
#0: ffffffff82dbaab0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x19/0x40
#1: ffffffff82dad0a8 (rtnl_mutex){+.+.}-{3:3}, at:
ethnl_default_set_doit+0xbe/0x1e0
stack backtrace:
CPU: 6 PID: 962 Comm: ethtool Not tainted 6.9.0-rc7+ #319
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x79/0xb0
check_deadlock+0x130/0x220
__lock_acquire+0x861/0x990
lock_acquire.part.0+0x72/0x1d0
? lock_acquire+0xf8/0x130
__mutex_lock+0x71/0xd50
virtnet_set_coalesce+0x151/0x190
__ethnl_set_coalesce.isra.0+0x3f8/0x4d0
ethnl_set_coalesce+0x34/0x90
ethnl_default_set_doit+0xdd/0x1e0
genl_family_rcv_msg_doit+0xdc/0x130
genl_family_rcv_msg+0x154/0x230
? __pfx_ethnl_default_set_doit+0x10/0x10
genl_rcv_msg+0x4b/0xa0
? __pfx_genl_rcv_msg+0x10/0x10
netlink_rcv_skb+0x5a/0x110
genl_rcv+0x28/0x40
netlink_unicast+0x1af/0x280
netlink_sendmsg+0x20e/0x460
__sys_sendto+0x1fe/0x210
? find_held_lock+0x2b/0x80
? do_user_addr_fault+0x3a2/0x8a0
? __lock_release+0x5e/0x160
? do_user_addr_fault+0x3a2/0x8a0
? lock_release+0x72/0x140
? do_user_addr_fault+0x3a7/0x8a0
__x64_sys_sendto+0x29/0x30
do_syscall_64+0x78/0x180
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Fixes: 4d4ac2ececd3 ("virtio_net: Add a lock for per queue RX coalesce")
Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 36 ++++++++++++++++--------------------
1 file changed, 16 insertions(+), 20 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4f828a9e5889..ecb5203d0372 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -4257,7 +4257,6 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
struct virtio_net_ctrl_coal_rx *coal_rx __free(kfree) = NULL;
bool rx_ctrl_dim_on = !!ec->use_adaptive_rx_coalesce;
struct scatterlist sgs_rx;
- int ret = 0;
int i;
if (rx_ctrl_dim_on && !virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL))
@@ -4267,27 +4266,27 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
ec->rx_max_coalesced_frames != vi->intr_coal_rx.max_packets))
return -EINVAL;
- /* Acquire all queues dim_locks */
- for (i = 0; i < vi->max_queue_pairs; i++)
- mutex_lock(&vi->rq[i].dim_lock);
-
if (rx_ctrl_dim_on && !vi->rx_dim_enabled) {
vi->rx_dim_enabled = true;
- for (i = 0; i < vi->max_queue_pairs; i++)
+ for (i = 0; i < vi->max_queue_pairs; i++) {
+ mutex_lock(&vi->rq[i].dim_lock);
vi->rq[i].dim_enabled = true;
- goto unlock;
+ mutex_unlock(&vi->rq[i].dim_lock);
+ }
+ return 0;
}
coal_rx = kzalloc(sizeof(*coal_rx), GFP_KERNEL);
- if (!coal_rx) {
- ret = -ENOMEM;
- goto unlock;
- }
+ if (!coal_rx)
+ return -ENOMEM;
if (!rx_ctrl_dim_on && vi->rx_dim_enabled) {
vi->rx_dim_enabled = false;
- for (i = 0; i < vi->max_queue_pairs; i++)
+ for (i = 0; i < vi->max_queue_pairs; i++) {
+ mutex_lock(&vi->rq[i].dim_lock);
vi->rq[i].dim_enabled = false;
+ mutex_unlock(&vi->rq[i].dim_lock);
+ }
}
/* Since the per-queue coalescing params can be set,
@@ -4300,22 +4299,19 @@ static int virtnet_send_rx_notf_coal_cmds(struct virtnet_info *vi,
if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_NOTF_COAL,
VIRTIO_NET_CTRL_NOTF_COAL_RX_SET,
- &sgs_rx)) {
- ret = -EINVAL;
- goto unlock;
- }
+ &sgs_rx))
+ return -EINVAL;
vi->intr_coal_rx.max_usecs = ec->rx_coalesce_usecs;
vi->intr_coal_rx.max_packets = ec->rx_max_coalesced_frames;
for (i = 0; i < vi->max_queue_pairs; i++) {
+ mutex_lock(&vi->rq[i].dim_lock);
vi->rq[i].intr_coal.max_usecs = ec->rx_coalesce_usecs;
vi->rq[i].intr_coal.max_packets = ec->rx_max_coalesced_frames;
- }
-unlock:
- for (i = vi->max_queue_pairs - 1; i >= 0; i--)
mutex_unlock(&vi->rq[i].dim_lock);
+ }
- return ret;
+ return 0;
}
static int virtnet_send_notf_coal_cmds(struct virtnet_info *vi,
--
2.32.0.3.g01195cf9f
