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    Subject[PATCH 3.18 041/145] [PATCH 087/760] net: pktgen: remove rcu locking in pktgen_change_name()
    Date
    3.18-stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Dumazet <edumazet@google.com>


    [ Upstream commit 9a0b1e8ba4061778897b544afc898de2163382f7 ]

    After Jesper commit back in linux-3.18, we trigger a lockdep
    splat in proc_create_data() while allocating memory from
    pktgen_change_name().

    This patch converts t->if_lock to a mutex, since it is now only
    used from control path, and adds proper locking to pktgen_change_name()

    1) pktgen_thread_lock to protect the outer loop (iterating threads)
    2) t->if_lock to protect the inner loop (iterating devices)

    Note that before Jesper patch, pktgen_change_name() was lacking proper
    protection, but lockdep was not able to detect the problem.

    Fixes: 8788370a1d4b ("pktgen: RCU-ify "if_list" to remove lock in next_to_run()")
    Reported-by: John Sperbeck <jsperbeck@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Jesper Dangaard Brouer <brouer@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/core/pktgen.c | 17 ++++++++++-------
    1 file changed, 10 insertions(+), 7 deletions(-)

    --- a/net/core/pktgen.c
    +++ b/net/core/pktgen.c
    @@ -211,8 +211,8 @@
    #define T_REMDEV (1<<3) /* Remove one dev */

    /* If lock -- protects updating of if_list */
    -#define if_lock(t) spin_lock(&(t->if_lock));
    -#define if_unlock(t) spin_unlock(&(t->if_lock));
    +#define if_lock(t) mutex_lock(&(t->if_lock));
    +#define if_unlock(t) mutex_unlock(&(t->if_lock));

    /* Used to help with determining the pkts on receive */
    #define PKTGEN_MAGIC 0xbe9be955
    @@ -418,7 +418,7 @@ struct pktgen_net {
    };

    struct pktgen_thread {
    - spinlock_t if_lock; /* for list of devices */
    + struct mutex if_lock; /* for list of devices */
    struct list_head if_list; /* All device here */
    struct list_head th_list;
    struct task_struct *tsk;
    @@ -1952,11 +1952,13 @@ static void pktgen_change_name(const str
    {
    struct pktgen_thread *t;

    + mutex_lock(&pktgen_thread_lock);
    +
    list_for_each_entry(t, &pn->pktgen_threads, th_list) {
    struct pktgen_dev *pkt_dev;

    - rcu_read_lock();
    - list_for_each_entry_rcu(pkt_dev, &t->if_list, list) {
    + if_lock(t);
    + list_for_each_entry(pkt_dev, &t->if_list, list) {
    if (pkt_dev->odev != dev)
    continue;

    @@ -1971,8 +1973,9 @@ static void pktgen_change_name(const str
    dev->name);
    break;
    }
    - rcu_read_unlock();
    + if_unlock(t);
    }
    + mutex_unlock(&pktgen_thread_lock);
    }

    static int pktgen_device_event(struct notifier_block *unused,
    @@ -3656,7 +3659,7 @@ static int __net_init pktgen_create_thre
    return -ENOMEM;
    }

    - spin_lock_init(&t->if_lock);
    + mutex_init(&t->if_lock);
    t->cpu = cpu;

    INIT_LIST_HEAD(&t->if_list);

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