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    Subject[PATCH tip/core/rcu 3/3] Fix thinko in commit #de078d875, actually initialize full tree
    Date
    From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    Commit #de078d875 repeatedly and incorrectly initializes the root rcu_node
    structure's ->gpnum field rather than initializing the ->gpnum field of
    each node in the tree. Fix this. Also add an additional consistency
    check to catch this in the future.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcutree.c | 11 ++++-------
    kernel/rcutree_plugin.h | 4 +++-
    2 files changed, 7 insertions(+), 8 deletions(-)

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index 30e0e91..dd6e743 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -596,8 +596,6 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
    {
    struct rcu_data *rdp = rsp->rda[smp_processor_id()];
    struct rcu_node *rnp = rcu_get_root(rsp);
    - struct rcu_node *rnp_cur;
    - struct rcu_node *rnp_end;

    if (!cpu_needs_another_gp(rsp, rdp)) {
    spin_unlock_irqrestore(&rnp->lock, flags);
    @@ -654,13 +652,12 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
    * one corresponding to this CPU, due to the fact that we have
    * irqs disabled.
    */
    - rnp_end = &rsp->node[NUM_RCU_NODES];
    - for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) {
    - spin_lock(&rnp_cur->lock); /* irqs already disabled. */
    + for (rnp = &rsp->node[0]; rnp < &rsp->node[NUM_RCU_NODES]; rnp++) {
    + spin_lock(&rnp->lock); /* irqs already disabled. */
    rcu_preempt_check_blocked_tasks(rnp);
    - rnp_cur->qsmask = rnp_cur->qsmaskinit;
    + rnp->qsmask = rnp->qsmaskinit;
    rnp->gpnum = rsp->gpnum;
    - spin_unlock(&rnp_cur->lock); /* irqs already disabled. */
    + spin_unlock(&rnp->lock); /* irqs already disabled. */
    }

    rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index a2d586c..55c6497 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -476,10 +476,12 @@ static void rcu_print_task_stall(struct rcu_node *rnp)

    /*
    * Because there is no preemptable RCU, there can be no readers blocked,
    - * so there is no need to check for blocked tasks.
    + * so there is no need to check for blocked tasks. So check only for
    + * bogus qsmask values.
    */
    static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
    {
    + WARN_ON_ONCE(rnp->qsmask);
    }

    /*
    --
    1.5.2.5


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