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    Subject[PATCH] cpuidle: avoid using smp_processor_id() in preemptible code (nr_iowait_cpu) v4
    Fix

    BUG: using smp_processor_id() in preemptible [00000000] code: s2disk/3392
    caller is nr_iowait_cpu+0xe/0x1e
    Pid: 3392, comm: s2disk Not tainted 2.6.35-rc3-dbg-00106-ga75e02b #2
    Call Trace:
    [<c1184c55>] debug_smp_processor_id+0xa5/0xbc
    [<c10282a5>] nr_iowait_cpu+0xe/0x1e
    [<c104ab7c>] update_ts_time_stats+0x32/0x6c
    [<c104ac73>] get_cpu_idle_time_us+0x36/0x58
    [<c124229b>] get_cpu_idle_time+0x12/0x74
    [<c1242963>] cpufreq_governor_dbs+0xc3/0x2dc
    [<c1240437>] __cpufreq_governor+0x51/0x85
    [<c1241190>] __cpufreq_set_policy+0x10c/0x13d
    [<c12413d3>] cpufreq_add_dev_interface+0x212/0x233
    [<c1241b1e>] ? handle_update+0x0/0xd
    [<c1241a18>] cpufreq_add_dev+0x34b/0x35a
    [<c103c973>] ? schedule_delayed_work_on+0x11/0x13
    [<c12c14db>] cpufreq_cpu_callback+0x59/0x63
    [<c1042f39>] notifier_call_chain+0x26/0x48
    [<c1042f7d>] __raw_notifier_call_chain+0xe/0x10
    [<c102efb9>] __cpu_notify+0x15/0x29
    [<c102efda>] cpu_notify+0xd/0xf
    [<c12bfb30>] _cpu_up+0xaf/0xd2
    [<c12b3ad4>] enable_nonboot_cpus+0x3d/0x94
    [<c1055eef>] hibernation_snapshot+0x104/0x1a2
    [<c1058b49>] snapshot_ioctl+0x24b/0x53e
    [<c1028ad1>] ? sub_preempt_count+0x7c/0x89
    [<c10ab91d>] vfs_ioctl+0x2e/0x8c
    [<c10588fe>] ? snapshot_ioctl+0x0/0x53e
    [<c10ac2c7>] do_vfs_ioctl+0x42f/0x45a
    [<c10a0ba5>] ? fsnotify_modify+0x4f/0x5a
    [<c11e9dc3>] ? tty_write+0x0/0x1d0
    [<c10a12d6>] ? vfs_write+0xa2/0xda
    [<c10ac333>] sys_ioctl+0x41/0x62
    [<c10027d3>] sysenter_do_call+0x12/0x2d

    The initial fix was to use get_cpu/put_cpu in nr_iowait_cpu. However,
    Arjan stated that "the bug is that it needs to be nr_iowait_cpu(int cpu)".

    This patch introduces nr_iowait_cpu(int cpu) and changes to its callers.

    Arjan also pointed out that we can't use get_cpu/put_cpu in update_ts_time_stats
    since we "pick the current cpu, rather than the one denoted by ts" in that case.
    To match given *ts and cpu denoted by *ts we use new field in the struct tick_sched: int cpu.

    Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

    ---

    diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
    index 52ff8aa..4871ed5 100644
    --- a/drivers/cpuidle/governors/menu.c
    +++ b/drivers/cpuidle/governors/menu.c
    @@ -137,14 +137,17 @@ static inline int which_bucket(unsigned int duration)
    {
    int bucket = 0;

    + int cpu = get_cpu();
    /*
    * We keep two groups of stats; one with no
    * IO pending, one without.
    * This allows us to calculate
    * E(duration)|iowait
    */
    - if (nr_iowait_cpu())
    + if (nr_iowait_cpu(cpu))
    bucket = BUCKETS/2;
    +
    + put_cpu();

    if (duration < 10)
    return bucket;
    @@ -169,14 +172,17 @@ static inline int which_bucket(unsigned int duration)
    static inline int performance_multiplier(void)
    {
    int mult = 1;
    -
    + int cpu = get_cpu();
    +
    /* for higher loadavg, we are more reluctant */

    mult += 2 * get_loadavg();

    /* for IO wait tasks (per cpu!) we add 5x each */
    - mult += 10 * nr_iowait_cpu();
    + mult += 10 * nr_iowait_cpu(cpu);

    + put_cpu();
    +
    return mult;
    }

    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index f118809..747fcae 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -139,7 +139,7 @@ extern int nr_processes(void);
    extern unsigned long nr_running(void);
    extern unsigned long nr_uninterruptible(void);
    extern unsigned long nr_iowait(void);
    -extern unsigned long nr_iowait_cpu(void);
    +extern unsigned long nr_iowait_cpu(int cpu);
    extern unsigned long this_cpu_load(void);


    diff --git a/include/linux/tick.h b/include/linux/tick.h
    index b232ccc..db14691 100644
    --- a/include/linux/tick.h
    +++ b/include/linux/tick.h
    @@ -51,6 +51,7 @@ struct tick_sched {
    unsigned long check_clocks;
    enum tick_nohz_mode nohz_mode;
    ktime_t idle_tick;
    + int cpu;
    int inidle;
    int tick_stopped;
    unsigned long idle_jiffies;
    diff --git a/kernel/sched.c b/kernel/sched.c
    index f8b8996..f61b48e 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -2864,9 +2864,9 @@ unsigned long nr_iowait(void)
    return sum;
    }

    -unsigned long nr_iowait_cpu(void)
    +unsigned long nr_iowait_cpu(int cpu)
    {
    - struct rq *this = this_rq();
    + struct rq *this = cpu_rq(cpu);
    return atomic_read(&this->nr_iowait);
    }

    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index 1d7b9bc..1907037 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -38,6 +38,9 @@ static ktime_t last_jiffies_update;

    struct tick_sched *tick_get_tick_sched(int cpu)
    {
    + /*FIXME: Arjan van de Ven:
    + can we do this bit once, when the ts structure gets initialized?*/
    + per_cpu(tick_cpu_sched, cpu).cpu = cpu;
    return &per_cpu(tick_cpu_sched, cpu);
    }

    @@ -137,7 +140,7 @@ __setup("nohz=", setup_tick_nohz);
    static void tick_nohz_update_jiffies(ktime_t now)
    {
    int cpu = smp_processor_id();
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    unsigned long flags;

    cpumask_clear_cpu(cpu, nohz_cpu_mask);
    @@ -161,7 +164,7 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)
    if (ts->idle_active) {
    delta = ktime_sub(now, ts->idle_entrytime);
    ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
    - if (nr_iowait_cpu() > 0)
    + if (nr_iowait_cpu(ts->cpu) > 0)
    ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
    ts->idle_entrytime = now;
    }
    @@ -173,7 +176,7 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)

    static void tick_nohz_stop_idle(int cpu, ktime_t now)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    update_ts_time_stats(ts, now, NULL);
    ts->idle_active = 0;
    @@ -211,7 +214,7 @@ static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
    */
    u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    if (!tick_nohz_enabled)
    return -1;
    @@ -237,7 +240,7 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
    */
    u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    if (!tick_nohz_enabled)
    return -1;
    @@ -267,7 +270,7 @@ void tick_nohz_stop_sched_tick(int inidle)
    local_irq_save(flags);

    cpu = smp_processor_id();
    - ts = &per_cpu(tick_cpu_sched, cpu);
    + ts = tick_get_tick_sched(cpu);

    /*
    * Call to tick_nohz_start_idle stops the last_update_time from being
    @@ -508,7 +511,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
    void tick_nohz_restart_sched_tick(void)
    {
    int cpu = smp_processor_id();
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    #ifndef CONFIG_VIRT_CPU_ACCOUNTING
    unsigned long ticks;
    #endif
    @@ -671,7 +674,7 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)
    #if 0
    /* Switch back to 2.6.27 behaviour */

    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    ktime_t delta;

    /*
    @@ -688,7 +691,7 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)

    static inline void tick_check_nohz(int cpu)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);
    ktime_t now;

    if (!ts->idle_active && !ts->tick_stopped)
    @@ -818,7 +821,7 @@ void tick_setup_sched_timer(void)
    #if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
    void tick_cancel_sched_timer(int cpu)
    {
    - struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
    + struct tick_sched *ts = tick_get_tick_sched(cpu);

    # ifdef CONFIG_HIGH_RES_TIMERS
    if (ts->sched_timer.base)



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