net: dcb: disable softirqs in dcbnl_flush_dev()

BugLink: https://bugs.launchpad.net/bugs/1964361
[ Upstream commit 10b6bb62ae1a49ee818fc479cf57b8900176773e ]

Ido Schimmel points out that since commit 52cff74eef5d ("dcbnl : Disable
software interrupts before taking dcb_lock"), the DCB API can be called
by drivers from softirq context.

One such in-tree example is the chelsio cxgb4 driver:
dcb_rpl
-> cxgb4_dcb_handle_fw_update
   -> dcb_ieee_setapp

If the firmware for this driver happened to send an event which resulted
in a call to dcb_ieee_setapp() at the exact same time as another
DCB-enabled interface was unregistering on the same CPU, the softirq
would deadlock, because the interrupted process was already holding the
dcb_lock in dcbnl_flush_dev().

Fix this unlikely event by using spin_lock_bh() in dcbnl_flush_dev() as
in the rest of the dcbnl code.

Fixes: 91b0383fef06 ("net: dcb: flush lingering app table entries for unregistered devices")
Reported-by: Ido Schimmel <idosch@idosch.org>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20220302193939.1368823-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/net/dcb/dcbnl.c b/net/dcb/dcbnl.c
index 36c91273daac5b2b6a9b3cb0d99d3d833db7f90e..dc4fb699b56c3adc3340e336c9924472374d0d0a 100644 (file)
--- a/net/dcb/dcbnl.c
+++ b/net/dcb/dcbnl.c
@@ -2077,7 +2077,7 @@ static void dcbnl_flush_dev(struct net_device *dev)
 {
        struct dcb_app_type *itr, *tmp;
 
-       spin_lock(&dcb_lock);
+       spin_lock_bh(&dcb_lock);
 
        list_for_each_entry_safe(itr, tmp, &dcb_app_list, list) {
                if (itr->ifindex == dev->ifindex) {
@@ -2086,7 +2086,7 @@ static void dcbnl_flush_dev(struct net_device *dev)
                }
        }
 
-       spin_unlock(&dcb_lock);
+       spin_unlock_bh(&dcb_lock);
 }
 
 static int dcbnl_netdevice_event(struct notifier_block *nb,