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    SubjectRe: [PATCH v9 5/7] tracing: Centralize preemptirq tracepoints and unify their usage
    On Thu, Jun 28, 2018 at 11:21:47AM -0700, Joel Fernandes wrote:
    > One note, I have to check for lockdep recursion in the code that calls
    > the trace events API and bail out if we're in lockdep recursion

    I'm not seeing any new lockdep_recursion checks...

    > protection to prevent something like the following case: a spin_lock is
    > taken. Then lockdep_acquired is called. That does a raw_local_irq_save
    > and then sets lockdep_recursion, and then calls __lockdep_acquired. In
    > this function, a call to get_lock_stats happens which calls
    > preempt_disable, which calls trace IRQS off somewhere which enters my
    > tracepoint code and sets the tracing_irq_cpu flag to prevent recursion.
    > This flag is then never cleared causing lockdep paths to never be
    > entered and thus causing splats and other bad things.

    Would it not be much easier to avoid that entirely, afaict all
    get/put_lock_stats() callers already have IRQs disabled, so that
    (traced) preempt fiddling is entirely superfluous.

    ---
    diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
    index 5fa4d3138bf1..8f5ce0048d15 100644
    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -248,12 +248,7 @@ void clear_lock_stats(struct lock_class *class)

    static struct lock_class_stats *get_lock_stats(struct lock_class *class)
    {
    - return &get_cpu_var(cpu_lock_stats)[class - lock_classes];
    -}
    -
    -static void put_lock_stats(struct lock_class_stats *stats)
    -{
    - put_cpu_var(cpu_lock_stats);
    + return &this_cpu_ptr(&cpu_lock_stats)[class - lock_classes];
    }

    static void lock_release_holdtime(struct held_lock *hlock)
    @@ -271,7 +266,6 @@ static void lock_release_holdtime(struct held_lock *hlock)
    lock_time_inc(&stats->read_holdtime, holdtime);
    else
    lock_time_inc(&stats->write_holdtime, holdtime);
    - put_lock_stats(stats);
    }
    #else
    static inline void lock_release_holdtime(struct held_lock *hlock)
    @@ -4090,7 +4084,6 @@ __lock_contended(struct lockdep_map *lock, unsigned long ip)
    stats->contending_point[contending_point]++;
    if (lock->cpu != smp_processor_id())
    stats->bounces[bounce_contended + !!hlock->read]++;
    - put_lock_stats(stats);
    }

    static void
    @@ -4138,7 +4131,6 @@ __lock_acquired(struct lockdep_map *lock, unsigned long ip)
    }
    if (lock->cpu != cpu)
    stats->bounces[bounce_acquired + !!hlock->read]++;
    - put_lock_stats(stats);

    lock->cpu = cpu;
    lock->ip = ip;
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      Last update: 2018-07-11 15:13    [W:3.634 / U:0.008 seconds]
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