This is a note to let you know that I've just added the patch titled bridge: disable softirqs around br_fdb_update to avoid lockup to the 4.0-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bridge-disable-softirqs-around-br_fdb_update-to-avoid-lockup.patch and it can be found in the queue-4.0 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Sat Jun 13 09:48:35 PDT 2015 From: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx> Date: Sat, 6 Jun 2015 06:49:00 -0700 Subject: bridge: disable softirqs around br_fdb_update to avoid lockup 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(); rcu_read_lock(); br_fdb_update(p->br, p, addr, vid, true); rcu_read_unlock(); + local_bh_enable(); } else { spin_lock_bh(&p->br->hash_lock); err = fdb_add_entry(p, addr, ndm->ndm_state, Patches currently in stable-queue which might be from nikolay@xxxxxxxxxxxxxxxxxxx are queue-4.0/bridge-disable-softirqs-around-br_fdb_update-to-avoid-lockup.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html