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    Subject[tip:core/rcu] rcu: Add RCU_CPU_STALL_VERBOSE to dump detailed per-task information
    Commit-ID:  1ed509a225008c9e8c0644fbd22168e09a7383a0
    Gitweb: http://git.kernel.org/tip/1ed509a225008c9e8c0644fbd22168e09a7383a0
    Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    AuthorDate: Mon, 22 Feb 2010 17:05:05 -0800
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Thu, 25 Feb 2010 10:35:02 +0100

    rcu: Add RCU_CPU_STALL_VERBOSE to dump detailed per-task information

    When RCU detects a grace-period stall, it currently just prints
    out the PID of any tasks doing the stalling. This patch adds
    RCU_CPU_STALL_VERBOSE, which enables the more-verbose reporting
    from sched_show_task().

    Suggested-by: Thomas Gleixner <tglx@linutronix.de>
    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: <1266887105-1528-21-git-send-email-paulmck@linux.vnet.ibm.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    kernel/rcutree.c | 4 +++
    kernel/rcutree.h | 1 +
    kernel/rcutree_plugin.h | 52 +++++++++++++++++++++++++++++++++++++++++++++++
    lib/Kconfig.debug | 12 ++++++++++
    4 files changed, 69 insertions(+), 0 deletions(-)

    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index b07be37..525d398 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -489,6 +489,10 @@ static void print_other_cpu_stall(struct rcu_state *rsp)
    smp_processor_id(), (long)(jiffies - rsp->gp_start));
    trigger_all_cpu_backtrace();

    + /* If so configured, complain about tasks blocking the grace period. */
    +
    + rcu_print_detail_task_stall(rsp);
    +
    force_quiescent_state(rsp, 0); /* Kick them all. */
    }

    diff --git a/kernel/rcutree.h b/kernel/rcutree.h
    index 6a82c34..2ceb083 100644
    --- a/kernel/rcutree.h
    +++ b/kernel/rcutree.h
    @@ -352,6 +352,7 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp,
    unsigned long flags);
    #endif /* #ifdef CONFIG_HOTPLUG_CPU */
    #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
    +static void rcu_print_detail_task_stall(struct rcu_state *rsp);
    static void rcu_print_task_stall(struct rcu_node *rnp);
    #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
    static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp);
    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index aecfe37..3516de7 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -312,6 +312,50 @@ EXPORT_SYMBOL_GPL(__rcu_read_unlock);

    #ifdef CONFIG_RCU_CPU_STALL_DETECTOR

    +#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
    +
    +/*
    + * Dump detailed information for all tasks blocking the current RCU
    + * grace period on the specified rcu_node structure.
    + */
    +static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
    +{
    + unsigned long flags;
    + struct list_head *lp;
    + int phase;
    + struct task_struct *t;
    +
    + if (rcu_preempted_readers(rnp)) {
    + raw_spin_lock_irqsave(&rnp->lock, flags);
    + phase = rnp->gpnum & 0x1;
    + lp = &rnp->blocked_tasks[phase];
    + list_for_each_entry(t, lp, rcu_node_entry)
    + sched_show_task(t);
    + raw_spin_unlock_irqrestore(&rnp->lock, flags);
    + }
    +}
    +
    +/*
    + * Dump detailed information for all tasks blocking the current RCU
    + * grace period.
    + */
    +static void rcu_print_detail_task_stall(struct rcu_state *rsp)
    +{
    + struct rcu_node *rnp = rcu_get_root(rsp);
    +
    + rcu_print_detail_task_stall_rnp(rnp);
    + rcu_for_each_leaf_node(rsp, rnp)
    + rcu_print_detail_task_stall_rnp(rnp);
    +}
    +
    +#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
    +
    +static void rcu_print_detail_task_stall(struct rcu_state *rsp)
    +{
    +}
    +
    +#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
    +
    /*
    * Scan the current list of tasks blocked within RCU read-side critical
    * sections, printing out the tid of each.
    @@ -764,6 +808,14 @@ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
    * Because preemptable RCU does not exist, we never have to check for
    * tasks blocked within RCU read-side critical sections.
    */
    +static void rcu_print_detail_task_stall(struct rcu_state *rsp)
    +{
    +}
    +
    +/*
    + * Because preemptable RCU does not exist, we never have to check for
    + * tasks blocked within RCU read-side critical sections.
    + */
    static void rcu_print_task_stall(struct rcu_node *rnp)
    {
    }
    diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
    index 6af20a8..4cdab45 100644
    --- a/lib/Kconfig.debug
    +++ b/lib/Kconfig.debug
    @@ -781,6 +781,18 @@ config RCU_CPU_STALL_DETECTOR

    Say Y if you are unsure.

    +config RCU_CPU_STALL_VERBOSE
    + bool "Print additional per-task information for RCU_CPU_STALL_DETECTOR"
    + depends on RCU_CPU_STALL_DETECTOR && TREE_PREEMPT_RCU
    + default n
    + help
    + This option causes RCU to printk detailed per-task information
    + for any tasks that are stalling the current RCU grace period.
    +
    + Say N if you are unsure.
    +
    + Say Y if you want to enable such checks.
    +
    config KPROBES_SANITY_TEST
    bool "Kprobes sanity tests"
    depends on DEBUG_KERNEL

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