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    Subject[tip:core/rcu] rcu: Stopgap fix for synchronize_rcu_expedited() for TREE_PREEMPT_RCU
    Commit-ID:  019129d595caaa5bd0b41d128308da1be6a91869
    Gitweb: http://git.kernel.org/tip/019129d595caaa5bd0b41d128308da1be6a91869
    Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    AuthorDate: Wed, 14 Oct 2009 10:15:56 -0700
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Thu, 15 Oct 2009 11:17:17 +0200

    rcu: Stopgap fix for synchronize_rcu_expedited() for TREE_PREEMPT_RCU

    For the short term, map synchronize_rcu_expedited() to
    synchronize_rcu() for TREE_PREEMPT_RCU and to
    synchronize_sched_expedited() for TREE_RCU.

    Longer term, there needs to be a real expedited grace period for
    TREE_PREEMPT_RCU, but candidate patches to date are considerably
    more complex and intrusive.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: laijs@cn.fujitsu.com
    Cc: dipankar@in.ibm.com
    Cc: mathieu.desnoyers@polymtl.ca
    Cc: josh@joshtriplett.org
    Cc: dvhltc@us.ibm.com
    Cc: niv@us.ibm.com
    Cc: peterz@infradead.org
    Cc: rostedt@goodmis.org
    Cc: Valdis.Kletnieks@vt.edu
    Cc: dhowells@redhat.com
    Cc: npiggin@suse.de
    Cc: jens.axboe@oracle.com
    LKML-Reference: <12555405592331-git-send-email->
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    include/linux/rcutree.h | 6 +-----
    kernel/rcutree_plugin.h | 21 +++++++++++++++++++++
    2 files changed, 22 insertions(+), 5 deletions(-)

    diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
    index 46e9ab3..9642c6b 100644
    --- a/include/linux/rcutree.h
    +++ b/include/linux/rcutree.h
    @@ -76,11 +76,7 @@ static inline void __rcu_read_unlock_bh(void)

    extern void call_rcu_sched(struct rcu_head *head,
    void (*func)(struct rcu_head *rcu));
    -
    -static inline void synchronize_rcu_expedited(void)
    -{
    - synchronize_sched_expedited();
    -}
    +extern void synchronize_rcu_expedited(void);

    static inline void synchronize_rcu_bh_expedited(void)
    {
    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index c0cb783..ebd20ee 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -393,6 +393,17 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
    EXPORT_SYMBOL_GPL(call_rcu);

    /*
    + * Wait for an rcu-preempt grace period. We are supposed to expedite the
    + * grace period, but this is the crude slow compatability hack, so just
    + * invoke synchronize_rcu().
    + */
    +void synchronize_rcu_expedited(void)
    +{
    + synchronize_rcu();
    +}
    +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
    +
    +/*
    * Check to see if there is any immediate preemptable-RCU-related work
    * to be done.
    */
    @@ -565,6 +576,16 @@ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
    EXPORT_SYMBOL_GPL(call_rcu);

    /*
    + * Wait for an rcu-preempt grace period, but make it happen quickly.
    + * But because preemptable RCU does not exist, map to rcu-sched.
    + */
    +void synchronize_rcu_expedited(void)
    +{
    + synchronize_sched_expedited();
    +}
    +EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
    +
    +/*
    * Because preemptable RCU does not exist, it never has any work to do.
    */
    static int rcu_preempt_pending(int cpu)

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