Commit 1d7c4903 authored Jun 05, 2015 by Wilson Kok Committed by David S. Miller Jun 07, 2015

bridge: use _bh spinlock variant for br_fdb_update to avoid lockup



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 use spin_lock_bh 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. These locks were _bh before commit f8ae737d
("[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:
292d1398 ("bridge: add NTF_USE support")

Signed-off-by: Wilson Kok <wkok@cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Fixes: 292d1398 ("bridge: add NTF_USE support")
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 078b29d7

net/bridge/br_fdb.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -569,7 +569,7 @@ void br_fdb_update(struct net_bridge br, struct net_bridge_port source,
		fdb_notify(br, fdb, RTM_NEWNEIGH);
		}
		} else {
		spin_lock(&br->hash_lock);
		spin_lock_bh(&br->hash_lock);
		if (likely(!fdb_find(head, addr, vid))) {
		fdb = fdb_create(head, source, addr, vid);
		if (fdb) {
		@@ -581,7 +581,7 @@ void br_fdb_update(struct net_bridge br, struct net_bridge_port source,
		/* else we lose race and someone else inserts
		* it first, don't bother updating
		*/
		spin_unlock(&br->hash_lock);
		spin_unlock_bh(&br->hash_lock);
		}
		}

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