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    Subject[GIT PULL] RCU fix
    Linus,

    Please pull the latest core-urgent-for-linus git tree from:

    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus

    HEAD: 40b3c43f042c2ba8915aff5c63708207ed7639cb Merge branch 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/urgent

    Thanks,

    Ingo

    ------------------>
    Paul E. McKenney (1):
    Revert "rcu: Move PREEMPT_RCU preemption to switch_to() invocation"


    arch/um/drivers/mconsole_kern.c | 1 -
    include/linux/rcupdate.h | 1 -
    include/linux/rcutiny.h | 6 ++++++
    include/linux/sched.h | 10 ----------
    kernel/rcutree.c | 1 +
    kernel/rcutree.h | 1 +
    kernel/rcutree_plugin.h | 14 +++++++++++---
    kernel/sched/core.c | 1 -
    8 files changed, 19 insertions(+), 16 deletions(-)

    diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
    index 88e466b..43b39d6 100644
    --- a/arch/um/drivers/mconsole_kern.c
    +++ b/arch/um/drivers/mconsole_kern.c
    @@ -705,7 +705,6 @@ static void stack_proc(void *arg)
    struct task_struct *from = current, *to = arg;

    to->thread.saved_task = from;
    - rcu_switch_from(from);
    switch_to(from, to, from);
    }

    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index 26d1a47..9cac722 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -184,7 +184,6 @@ static inline int rcu_preempt_depth(void)
    /* Internal to kernel */
    extern void rcu_sched_qs(int cpu);
    extern void rcu_bh_qs(int cpu);
    -extern void rcu_preempt_note_context_switch(void);
    extern void rcu_check_callbacks(int cpu, int user);
    struct notifier_block;
    extern void rcu_idle_enter(void);
    diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
    index 854dc4c..4e56a9c 100644
    --- a/include/linux/rcutiny.h
    +++ b/include/linux/rcutiny.h
    @@ -87,6 +87,10 @@ static inline void kfree_call_rcu(struct rcu_head *head,

    #ifdef CONFIG_TINY_RCU

    +static inline void rcu_preempt_note_context_switch(void)
    +{
    +}
    +
    static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
    {
    *delta_jiffies = ULONG_MAX;
    @@ -95,6 +99,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)

    #else /* #ifdef CONFIG_TINY_RCU */

    +void rcu_preempt_note_context_switch(void);
    int rcu_preempt_needs_cpu(void);

    static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
    @@ -108,6 +113,7 @@ static inline int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
    static inline void rcu_note_context_switch(int cpu)
    {
    rcu_sched_qs(cpu);
    + rcu_preempt_note_context_switch();
    }

    /*
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 4059c0f..06a4c5f 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -1871,22 +1871,12 @@ static inline void rcu_copy_process(struct task_struct *p)
    INIT_LIST_HEAD(&p->rcu_node_entry);
    }

    -static inline void rcu_switch_from(struct task_struct *prev)
    -{
    - if (prev->rcu_read_lock_nesting != 0)
    - rcu_preempt_note_context_switch();
    -}
    -
    #else

    static inline void rcu_copy_process(struct task_struct *p)
    {
    }

    -static inline void rcu_switch_from(struct task_struct *prev)
    -{
    -}
    -
    #endif

    #ifdef CONFIG_SMP
    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index 38ecdda..4b97bba 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -201,6 +201,7 @@ void rcu_note_context_switch(int cpu)
    {
    trace_rcu_utilization("Start context switch");
    rcu_sched_qs(cpu);
    + rcu_preempt_note_context_switch(cpu);
    trace_rcu_utilization("End context switch");
    }
    EXPORT_SYMBOL_GPL(rcu_note_context_switch);
    diff --git a/kernel/rcutree.h b/kernel/rcutree.h
    index ea05649..19b61ac 100644
    --- a/kernel/rcutree.h
    +++ b/kernel/rcutree.h
    @@ -444,6 +444,7 @@ DECLARE_PER_CPU(char, rcu_cpu_has_work);
    /* Forward declarations for rcutree_plugin.h */
    static void rcu_bootup_announce(void);
    long rcu_batches_completed(void);
    +static void rcu_preempt_note_context_switch(int cpu);
    static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp);
    #ifdef CONFIG_HOTPLUG_CPU
    static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index 5271a02..3e48994 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -153,7 +153,7 @@ static void rcu_preempt_qs(int cpu)
    *
    * Caller must disable preemption.
    */
    -void rcu_preempt_note_context_switch(void)
    +static void rcu_preempt_note_context_switch(int cpu)
    {
    struct task_struct *t = current;
    unsigned long flags;
    @@ -164,7 +164,7 @@ void rcu_preempt_note_context_switch(void)
    (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {

    /* Possibly blocking in an RCU read-side critical section. */
    - rdp = __this_cpu_ptr(rcu_preempt_state.rda);
    + rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
    rnp = rdp->mynode;
    raw_spin_lock_irqsave(&rnp->lock, flags);
    t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
    @@ -228,7 +228,7 @@ void rcu_preempt_note_context_switch(void)
    * means that we continue to block the current grace period.
    */
    local_irq_save(flags);
    - rcu_preempt_qs(smp_processor_id());
    + rcu_preempt_qs(cpu);
    local_irq_restore(flags);
    }

    @@ -1002,6 +1002,14 @@ void rcu_force_quiescent_state(void)
    EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);

    /*
    + * Because preemptible RCU does not exist, we never have to check for
    + * CPUs being in quiescent states.
    + */
    +static void rcu_preempt_note_context_switch(int cpu)
    +{
    +}
    +
    +/*
    * Because preemptible RCU does not exist, there are never any preempted
    * RCU readers.
    */
    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index d5594a4..eaead2d 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -2081,7 +2081,6 @@ context_switch(struct rq *rq, struct task_struct *prev,
    #endif

    /* Here we just switch the register state and the stack. */
    - rcu_switch_from(prev);
    switch_to(prev, next, prev);

    barrier();

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