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    SubjectRe: Regression: WARNINGS and lockdep spews in 2.6.38-rc3+ (bisected).
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    Date

    How about we revert your patch and go back to not allowing
    del_timer_sync() from any interrupt context, we can fix __dst_free by
    removing the need for cancel_delayed_work().

    Are there any other del_timer_sync() callers from softirq?

    ---
    include/linux/timer.h | 1 +
    kernel/timer.c | 67 ++++++++++++++++++++++++++++++------------------
    kernel/workqueue.c | 4 +-
    net/core/dst.c | 1 -
    4 files changed, 45 insertions(+), 28 deletions(-)

    diff --git a/include/linux/timer.h b/include/linux/timer.h
    index 6abd913..3e263f9 100644
    --- a/include/linux/timer.h
    +++ b/include/linux/timer.h
    @@ -209,6 +209,7 @@ static inline int timer_pending(const struct timer_list * timer)
    extern void add_timer_on(struct timer_list *timer, int cpu);
    extern int del_timer(struct timer_list * timer);
    extern int mod_timer(struct timer_list *timer, unsigned long expires);
    +extern int mod_timer_on(struct timer_list *timer, unsigned long expires, int cpu);
    extern int mod_timer_pending(struct timer_list *timer, unsigned long expires);
    extern int mod_timer_pinned(struct timer_list *timer, unsigned long expires);

    diff --git a/kernel/timer.c b/kernel/timer.c
    index 87f656c..c9e98f7 100644
    --- a/kernel/timer.c
    +++ b/kernel/timer.c
    @@ -648,8 +648,8 @@ static struct tvec_base *lock_timer_base(struct timer_list *timer,
    }

    static inline int
    -__mod_timer(struct timer_list *timer, unsigned long expires,
    - bool pending_only, int pinned)
    +__mod_timer_on(struct timer_list *timer, unsigned long expires,
    + bool pending_only, int pinned, int cpu)
    {
    struct tvec_base *base, *new_base;
    unsigned long flags;
    @@ -673,12 +673,14 @@ __mod_timer(struct timer_list *timer, unsigned long expires,

    debug_activate(timer, expires);

    - cpu = smp_processor_id();
    + if (cpu == -1) {
    + cpu = smp_processor_id();

    #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
    - if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
    - cpu = get_nohz_timer_target();
    + if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
    + cpu = get_nohz_timer_target();
    #endif
    + }
    new_base = per_cpu(tvec_bases, cpu);

    if (base != new_base) {
    @@ -705,12 +707,30 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
    base->next_timer = timer->expires;
    internal_add_timer(base, timer);

    + if (cpu != smp_processor_id()) {
    + /*
    + * Check whether the other CPU is idle and needs to be
    + * triggered to reevaluate the timer wheel when nohz is
    + * active. We are protected against the other CPU fiddling
    + * with the timer by holding the timer base lock. This also
    + * makes sure that a CPU on the way to idle can not evaluate
    + * the timer wheel.
    + */
    + wake_up_idle_cpu(cpu);
    + }
    out_unlock:
    spin_unlock_irqrestore(&base->lock, flags);

    return ret;
    }

    +static inline int
    +__mod_timer(struct timer_list *timer, unsigned long expires,
    + bool pending_only, int pinned)
    +{
    + return __mod_timer_on(timer, expires, pending_only, pinned, -1);
    +}
    +
    /**
    * mod_timer_pending - modify a pending timer's timeout
    * @timer: the pending timer to be modified
    @@ -825,6 +845,17 @@ int mod_timer_pinned(struct timer_list *timer, unsigned long expires)
    }
    EXPORT_SYMBOL(mod_timer_pinned);

    +int mod_timer_on(struct timer_list *timer, unsigned long expires, int cpu)
    +{
    + if (timer_pending(timer) && timer->expires == expires)
    + return 1;
    +
    + expires = apply_slack(timer, expires);
    +
    + return __mod_timer_on(timer, expires, false, TIMER_NOT_PINNED, cpu);
    +}
    +EXPORT_SYMBOL(mod_timer_on);
    +
    /**
    * add_timer - start a timer
    * @timer: the timer to be added
    @@ -860,23 +891,7 @@ void add_timer_on(struct timer_list *timer, int cpu)

    timer_stats_timer_set_start_info(timer);
    BUG_ON(timer_pending(timer) || !timer->function);
    - spin_lock_irqsave(&base->lock, flags);
    - timer_set_base(timer, base);
    - debug_activate(timer, timer->expires);
    - if (time_before(timer->expires, base->next_timer) &&
    - !tbase_get_deferrable(timer->base))
    - base->next_timer = timer->expires;
    - internal_add_timer(base, timer);
    - /*
    - * Check whether the other CPU is idle and needs to be
    - * triggered to reevaluate the timer wheel when nohz is
    - * active. We are protected against the other CPU fiddling
    - * with the timer by holding the timer base lock. This also
    - * makes sure that a CPU on the way to idle can not evaluate
    - * the timer wheel.
    - */
    - wake_up_idle_cpu(cpu);
    - spin_unlock_irqrestore(&base->lock, flags);
    + mod_timer_on(timer, timer->expires, cpu);
    }
    EXPORT_SYMBOL_GPL(add_timer_on);

    @@ -959,7 +974,7 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
    *
    * Synchronization rules: Callers must prevent restarting of the timer,
    * otherwise this function is meaningless. It must not be called from
    - * hardirq contexts. The caller must not hold locks which would prevent
    + * interrupt contexts. The caller must not hold locks which would prevent
    * completion of the timer's handler. The timer's handler must not call
    * add_timer_on(). Upon exit the timer is not queued and the handler is
    * not running on any CPU.
    @@ -969,10 +984,12 @@ EXPORT_SYMBOL(try_to_del_timer_sync);
    int del_timer_sync(struct timer_list *timer)
    {
    #ifdef CONFIG_LOCKDEP
    - local_bh_disable();
    + unsigned long flags;
    +
    + local_irq_save(flags);
    lock_map_acquire(&timer->lockdep_map);
    lock_map_release(&timer->lockdep_map);
    - local_bh_enable();
    + local_irq_restore(flags);
    #endif
    /*
    * don't use it in hardirq context, because it
    diff --git a/kernel/workqueue.c b/kernel/workqueue.c
    index 11869fa..3944acc 100644
    --- a/kernel/workqueue.c
    +++ b/kernel/workqueue.c
    @@ -1160,9 +1160,9 @@ int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
    timer->function = delayed_work_timer_fn;

    if (unlikely(cpu >= 0))
    - add_timer_on(timer, cpu);
    + mod_timer_on(timer, cpu);
    else
    - add_timer(timer);
    + mod_timer(timer);
    ret = 1;
    }
    return ret;
    diff --git a/net/core/dst.c b/net/core/dst.c
    index b99c7c7..a4f28bc 100644
    --- a/net/core/dst.c
    +++ b/net/core/dst.c
    @@ -207,7 +207,6 @@ void __dst_free(struct dst_entry *dst)
    if (dst_garbage.timer_inc > DST_GC_INC) {
    dst_garbage.timer_inc = DST_GC_INC;
    dst_garbage.timer_expires = DST_GC_MIN;
    - cancel_delayed_work(&dst_gc_work);
    schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
    }
    spin_unlock_bh(&dst_garbage.lock);



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