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    Subject[PATCH RFC tip/core/rcu 02/18] rcu: adjust force_quiescent_state() locking, step 2
    Date
    From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    Proposed for 2.6.34, not for inclusion.

    This patch releases rnp->lock after the end of force_quiescent_state()'s
    switch statement. This is a second step towards prohibiting starting
    grace periods while force_quiescent_state() is executing, which will
    reduce the number and complexity of races that force_quiescent_state()
    is involved in.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    ---
    kernel/rcutree.c | 13 +++----------
    1 files changed, 3 insertions(+), 10 deletions(-)

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index eae331d..d42ad30 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -1219,7 +1219,6 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
    case RCU_GP_IDLE:
    case RCU_GP_INIT:

    - spin_unlock(&rnp->lock);
    break; /* grace period idle or initializing, ignore. */

    case RCU_SAVE_DYNTICK:
    @@ -1246,10 +1245,8 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
    rsp->completed_fqs = lastcomp;
    forcenow = signaled == RCU_SAVE_COMPLETED;
    }
    - if (!forcenow) {
    - spin_unlock(&rnp->lock);
    + if (!forcenow)
    break;
    - }
    /* fall into next case. */

    case RCU_FORCE_QS:
    @@ -1262,14 +1259,10 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed)

    /* Leave state in case more forcing is required. */

    - break;
    -
    - default:
    -
    - spin_unlock(&rnp->lock);
    - WARN_ON_ONCE(1);
    + spin_lock(&rnp->lock);
    break;
    }
    + spin_unlock(&rnp->lock);
    unlock_fqs_ret:
    spin_unlock_irqrestore(&rsp->fqslock, flags);
    }
    --
    1.5.2.5


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