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    SubjectRe: [PATCH tip/core/rcu 3/3] rcu: place root rcu_node structure in separate lockdep class
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    On Tue, 2009-10-06 at 21:48 -0700, Paul E. McKenney wrote:
    > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >
    > Before this patch, all of the rcu_node structures were in the same lockdep
    > class, so that lockdep would complain when rcu_preempt_offline_tasks()
    > acquired the root rcu_node structure's lock while holding one of the leaf
    > rcu_nodes' locks. This patch changes rcu_init_one() to use a separate
    > spin_lock_init() for the root rcu_node structure's lock than is used for
    > that of all of the rest of the rcu_node structures, which puts the root
    > rcu_node structure's lock in its own lockdep class.
    >
    > Suggested-by: Peter Zijlstra <peterz@infradead.org>
    > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    > ---
    > kernel/rcutree.c | 4 +++-
    > 1 files changed, 3 insertions(+), 1 deletions(-)
    >
    > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    > index d8d9865..705f02a 100644
    > --- a/kernel/rcutree.c
    > +++ b/kernel/rcutree.c
    > @@ -1647,7 +1647,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
    > cpustride *= rsp->levelspread[i];
    > rnp = rsp->level[i];
    > for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
    > - spin_lock_init(&rnp->lock);
    > + if (rnp != rcu_get_root(rsp))
    > + spin_lock_init(&rnp->lock);
    > rnp->gpnum = 0;
    > rnp->qsmask = 0;
    > rnp->qsmaskinit = 0;
    > @@ -1670,6 +1671,7 @@ static void __init rcu_init_one(struct rcu_state *rsp)
    > INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
    > }
    > }
    > + spin_lock_init(&rcu_get_root(rsp)->lock);
    > }
    >
    > /*


    An alternative version that would not change any code in the !LOCKDEP
    case would read as:

    ---
    kernel/rcutree.c | 4 ++++
    1 files changed, 4 insertions(+), 0 deletions(-)

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index d8d9865..113f274 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -1625,6 +1625,8 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
    }
    #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */

    +static struct lock_class_key rcu_root_class;
    +
    /*
    * Helper function for rcu_init() that initializes one rcu_state structure.
    */
    @@ -1670,6 +1672,7 @@ static void __init rcu_init_one(struct rcu_state *rsp)
    INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
    }
    }
    + lockdep_set_class(&rcu_get_root(rsp)->lock, &rcu_root_class);
    }

    /*


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      Last update: 2009-10-08 11:37    [W:0.029 / U:0.444 seconds]
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