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    Subject[PATCH 3.4 128/146] bridge: use _bh spinlock variant for br_fdb_update to avoid lockup
    Date
    From: Wilson Kok <wkok@cumulusnetworks.com>

    3.4.109-rc1 review patch. If anyone has any objections, please let me know.

    ------------------


    commit 1d7c49037b12016e7056b9f2c990380e2187e766 upstream.

    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 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")

    Signed-off-by: Wilson Kok <wkok@cumulusnetworks.com>
    Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
    Fixes: 292d1398983f ("bridge: add NTF_USE support")
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [lizf: Backported to 3.4: adjust context]
    Signed-off-by: Zefan Li <lizefan@huawei.com>
    ---
    net/bridge/br_fdb.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
    index 5ba0c84..b5597bb 100644
    --- a/net/bridge/br_fdb.c
    +++ b/net/bridge/br_fdb.c
    @@ -440,7 +440,7 @@ void br_fdb_update(struct net_bridge *br, struct net_bridge_port *source,
    fdb->updated = jiffies;
    }
    } else {
    - spin_lock(&br->hash_lock);
    + spin_lock_bh(&br->hash_lock);
    if (likely(!fdb_find(head, addr))) {
    fdb = fdb_create(head, source, addr);
    if (fdb)
    @@ -449,7 +449,7 @@ 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);
    }
    }

    --
    1.9.1


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