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    Subject[tip:core/rcu] rcu: Add debug check for too many rcu_read_unlock()
    Commit-ID:  cba8244a0f1c277b6b1e48ed6504fa434119e24d
    Gitweb: http://git.kernel.org/tip/cba8244a0f1c277b6b1e48ed6504fa434119e24d
    Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    AuthorDate: Mon, 4 Jan 2010 16:04:01 -0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Wed, 13 Jan 2010 09:06:06 +0100

    rcu: Add debug check for too many rcu_read_unlock()

    TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in
    the task structure, which happens to be a signed int. So this
    patch adds a check for this counter being negative at the end of
    __rcu_read_unlock(). This check is under CONFIG_PROVE_LOCKING,
    so can be thought of as being part of lockdep.

    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
    LKML-Reference: <12626498423064-git-send-email->
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/rcutree_plugin.h | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index f11ebd4..e77cdf3 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
    if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
    rcu_read_unlock_special(t);
    +#ifdef CONFIG_PROVE_LOCKING
    + WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
    +#endif /* #ifdef CONFIG_PROVE_LOCKING */
    }
    EXPORT_SYMBOL_GPL(__rcu_read_unlock);


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