From fd888e85fe6b661e78044dddfec0be5271afa626 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Fri, 26 Nov 2021 17:15:29 +0100 Subject: net: Write lock dev_base_lock without disabling bottom halves. The writer acquires dev_base_lock with disabled bottom halves. The reader can acquire dev_base_lock without disabling bottom halves because there is no writer in softirq context. On PREEMPT_RT the softirqs are preemptible and local_bh_disable() acts as a lock to ensure that resources, that are protected by disabling bottom halves, remain protected. This leads to a circular locking dependency if the lock acquired with disabled bottom halves (as in write_lock_bh()) and somewhere else with enabled bottom halves (as by read_lock() in netstat_show()) followed by disabling bottom halves (cxgb_get_stats() -> t4_wr_mbox_meat_timeout() -> spin_lock_bh()). This is the reverse locking order. All read_lock() invocation are from sysfs callback which are not invoked from softirq context. Therefore there is no need to disable bottom halves while acquiring a write lock. Acquire the write lock of dev_base_lock without disabling bottom halves. Reported-by: Pei Zhang Reported-by: Luis Claudio R. Goncalves Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: David S. Miller --- net/core/rtnetlink.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'net/core/rtnetlink.c') diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index 6f25c0a8aebe..d6eba554b137 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -842,9 +842,9 @@ static void set_operstate(struct net_device *dev, unsigned char transition) } if (dev->operstate != operstate) { - write_lock_bh(&dev_base_lock); + write_lock(&dev_base_lock); dev->operstate = operstate; - write_unlock_bh(&dev_base_lock); + write_unlock(&dev_base_lock); netdev_state_change(dev); } } @@ -2778,11 +2778,11 @@ static int do_setlink(const struct sk_buff *skb, if (tb[IFLA_LINKMODE]) { unsigned char value = nla_get_u8(tb[IFLA_LINKMODE]); - write_lock_bh(&dev_base_lock); + write_lock(&dev_base_lock); if (dev->link_mode ^ value) status |= DO_SETLINK_NOTIFY; dev->link_mode = value; - write_unlock_bh(&dev_base_lock); + write_unlock(&dev_base_lock); } if (tb[IFLA_VFINFO_LIST]) { -- cgit