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    Subject[RFC][PATCH 18/26] srcu: revert2
        rcu: Add lockdep-RCU checks for simple self-deadlock

    It is illegal to have a grace period within a same-flavor RCU read-side
    critical section, so this commit adds lockdep-RCU checks to splat when
    such abuse is encountered. This commit does not detect more elaborate
    RCU deadlock situations. These situations might be a job for lockdep
    enhancements.

    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    kernel/rcutiny.c | 4 ----
    kernel/rcutiny_plugin.h | 5 -----
    kernel/rcutree.c | 8 --------
    kernel/rcutree_plugin.h | 4 ----
    kernel/srcu.c | 6 ------
    5 files changed, 27 deletions(-)

    --- a/kernel/rcutiny.c
    +++ b/kernel/rcutiny.c
    @@ -329,10 +329,6 @@ static void rcu_process_callbacks(struct
    */
    void synchronize_sched(void)
    {
    - rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
    - !lock_is_held(&rcu_lock_map) &&
    - !lock_is_held(&rcu_sched_lock_map),
    - "Illegal synchronize_sched() in RCU read-side critical section");
    cond_resched();
    }
    EXPORT_SYMBOL_GPL(synchronize_sched);
    --- a/kernel/rcutiny_plugin.h
    +++ b/kernel/rcutiny_plugin.h
    @@ -735,11 +735,6 @@ EXPORT_SYMBOL_GPL(call_rcu);
    */
    void synchronize_rcu(void)
    {
    - rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
    - !lock_is_held(&rcu_lock_map) &&
    - !lock_is_held(&rcu_sched_lock_map),
    - "Illegal synchronize_rcu() in RCU read-side critical section");
    -
    #ifdef CONFIG_DEBUG_LOCK_ALLOC
    if (!rcu_scheduler_active)
    return;
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -1919,10 +1919,6 @@ EXPORT_SYMBOL_GPL(call_rcu_bh);
    */
    void synchronize_sched(void)
    {
    - rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
    - !lock_is_held(&rcu_lock_map) &&
    - !lock_is_held(&rcu_sched_lock_map),
    - "Illegal synchronize_sched() in RCU-sched read-side critical section");
    if (rcu_blocking_is_gp())
    return;
    wait_rcu_gp(call_rcu_sched);
    @@ -1940,10 +1936,6 @@ EXPORT_SYMBOL_GPL(synchronize_sched);
    */
    void synchronize_rcu_bh(void)
    {
    - rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
    - !lock_is_held(&rcu_lock_map) &&
    - !lock_is_held(&rcu_sched_lock_map),
    - "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
    if (rcu_blocking_is_gp())
    return;
    wait_rcu_gp(call_rcu_bh);
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -731,10 +731,6 @@ EXPORT_SYMBOL_GPL(kfree_call_rcu);
    */
    void synchronize_rcu(void)
    {
    - rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
    - !lock_is_held(&rcu_lock_map) &&
    - !lock_is_held(&rcu_sched_lock_map),
    - "Illegal synchronize_rcu() in RCU read-side critical section");
    if (!rcu_scheduler_active)
    return;
    wait_rcu_gp(call_rcu);
    --- a/kernel/srcu.c
    +++ b/kernel/srcu.c
    @@ -172,12 +172,6 @@ static void __synchronize_srcu(struct sr
    {
    int idx;

    - rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
    - !lock_is_held(&rcu_bh_lock_map) &&
    - !lock_is_held(&rcu_lock_map) &&
    - !lock_is_held(&rcu_sched_lock_map),
    - "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
    -
    idx = sp->completed;
    mutex_lock(&sp->mutex);




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