Avoid a possible circular locking dependency by taking the softirq_ctrl.lock
before taking dev_base_lock in netstat_show(), keeping locking order
consistent.
Lockdep splat:
[ 106.529733] ======================================================
[ 106.529734] WARNING: possible circular locking dependency detected
[ 106.529734] 5.10.65-rt53+ #1 Tainted: G W I
[ 106.529736] ------------------------------------------------------
[ 106.529736] tuned/2760 is trying to acquire lock:
[ 106.529737] ffffa0695ea18220 ((softirq_ctrl.lock).lock){+.+.}-{2:2}, at: __local_bh_disable_ip+0x116/0x2f0
[ 106.529746]
but task is already holding lock:
[ 106.529746] ffffffff844af760 (dev_base_lock){++.+}-{0:0}, at: netstat_show.isra.17+0x4a/0xb0
[ 106.529752]
which lock already depends on the new lock.
...
[ 106.529825]
other info that might help us debug this:
[ 106.529826] Possible unsafe locking scenario:
[ 106.529826] CPU0 CPU1
[ 106.529827] ---- ----
[ 106.529827] lock(dev_base_lock);
[ 106.529828] lock((softirq_ctrl.lock).lock);
[ 106.529829] lock(dev_base_lock);
[ 106.529829] lock((softirq_ctrl.lock).lock);
[ 106.529830]
*** DEADLOCK ***
[ 106.529831] 6 locks held by tuned/2760:
[ 106.529832] #0: ffffa062296a6670 (&f->f_pos_lock){+.+.}-{0:0}, at: __fdget_pos+0x4b/0x60
[ 106.529836] #1: ffffa062223ae310 (&p->lock){+.+.}-{0:0}, at: seq_read_iter+0x56/0x420
[ 106.529839] #2: ffffa06242ea1ab8 (&of->mutex){+.+.}-{0:0}, at: kernfs_seq_start+0x28/0x90
[ 106.529842] #3: ffffa06268f52008 (kn->active#285){++++}-{0:0}, at: kernfs_seq_start+0x30/0x90
[ 106.529844] #4: ffffffff844af760 (dev_base_lock){++.+}-{0:0}, at: netstat_show.isra.17+0x4a/0xb0
[ 106.529848] #5: ffffffff840c8fa0 (rcu_read_lock){....}-{1:2}, at: rt_read_lock+0x7d/0x1e0
Reported-by: Pei Zhang <pezhang@xxxxxxxxxx>
Signed-off-by: Nitesh Narayan Lal <nilal@xxxxxxxxxx>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@xxxxxxxxxx>
---
net/core/net-sysfs.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index f6197774048b..7291ca052632 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -625,14 +625,14 @@ static ssize_t netstat_show(const struct device *d,
WARN_ON(offset > sizeof(struct rtnl_link_stats64) ||
offset % sizeof(u64) != 0);
- read_lock(&dev_base_lock);
+ read_lock_bh(&dev_base_lock);
if (dev_isalive(dev)) {
struct rtnl_link_stats64 temp;
const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
ret = sprintf(buf, fmt_u64, *(u64 *)(((u8 *)stats) + offset));
}
- read_unlock(&dev_base_lock);
+ read_unlock_bh(&dev_base_lock);
return ret;
}
