[PATCH 4.0 028/105] bridge: disable softirqs around br_fdb_update to avoid lockup

From: Greg Kroah-Hartman
Date: Fri Jun 19 2015 - 17:21:10 EST

4.0-stable review patch. If anyone has any objections, please let me know.


From: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit c4c832f89dc468cf11dc0dd17206bace44526651 ]

br_fdb_update() can be called in process context in the following way:
br_fdb_add() -> __br_fdb_add() -> br_fdb_update() (if NTF_USE flag is set)
so we need to disable softirqs because there are softirq users of the
hash_lock. One easy way to reproduce this is to modify the bridge utility
to set NTF_USE, enable stp and then set maxageing to a low value so
br_fdb_cleanup() is called frequently and then just add new entries in
a loop. This happens because br_fdb_cleanup() is called from timer/softirq
context. The spin locks in br_fdb_update were _bh before commit f8ae737deea1
("[BRIDGE]: forwarding remove unneeded preempt and bh diasables")
and at the time that commit was correct because br_fdb_update() couldn't be
called from process context, but that changed after commit:
292d1398983f ("bridge: add NTF_USE support")
Using local_bh_disable/enable around br_fdb_update() allows us to keep
using the spin_lock/unlock in br_fdb_update for the fast-path.

Signed-off-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
Fixes: 292d1398983f ("bridge: add NTF_USE support")
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/bridge/br_fdb.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -796,9 +796,11 @@ static int __br_fdb_add(struct ndmsg *nd
int err = 0;

if (ndm->ndm_flags & NTF_USE) {
+ local_bh_disable();
br_fdb_update(p->br, p, addr, vid, true);
+ local_bh_enable();
} else {
err = fdb_add_entry(p, addr, ndm->ndm_state,

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