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References: <20110421014153.126662477@goodmis.org>
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Date: Thu, 21 Apr 2011 15:08:28 +0800
Message-ID: <BANLkTimh79=gvOEsrHEmBox2LVUwM=LvLA@mail.gmail.com>
Subject: Re: [PATCH 1/7] lockdep: Print a nice description of an irq locking issue
From: Yong Zhang <yong.zhang0@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>
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On Thu, Apr 21, 2011 at 3:02 PM, Yong Zhang <yong.zhang0@gmail.com> wrote:
> On Thu, Apr 21, 2011 at 9:41 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
>>  ---
>>
>> The above is the case when the unsafe lock is taken while holding
>> a lock taken in irq context. But when a lock is taken that also
>> grabs a unsafe lock, the call chain is shown:
>>
>>  ---
>> other info that might help us debug this:
>>
>> Chain exists of:
>>  &rq->lock --> lockA --> lockC
>>
>>  Possible interrupt unsafe locking scenario:
>>
>>       CPU0                    CPU1
>>       ----                    ----
>>  lock(lockC);
>>                               local_irq_disable();
>>                               lock(&rq->lock);
>>                               lock(lockA);
>>  <Interrupt>
>>    lock(&rq->lock);
>>
>>  *** DEADLOCK ***
>
> Or we could show this:
> Chain exists of:
> &rq->lock --> lockA --> lockC
>
>  Possible interrupt unsafe locking scenario:
>
>      CPU0                    CPU1                           CPU2
>      ----                    ----                                     ----
>  lock(lockC);
>                              local_irq_disable();

                                                                Forget
 local_irq_disable(); here :)

>                              lock(&rq->lock);            lock(lockA);
>                              lock(lockA);                   lock(lockC);
>  <Interrupt>
>   lock(&rq->lock);
>
>  *** DEADLOCK ***
>
> Thanks,
> Yong
>
>>
>> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
>> ---
>>  kernel/lockdep.c |   70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>>  1 files changed, 70 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/lockdep.c b/kernel/lockdep.c
>> index 0d2058d..bb77c030 100644
>> --- a/kernel/lockdep.c
>> +++ b/kernel/lockdep.c
>> @@ -490,6 +490,18 @@ void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS])
>>        usage[i] = '\0';
>>  }
>>
>> +static int __print_lock_name(struct lock_class *class)
>> +{
>> +       char str[KSYM_NAME_LEN];
>> +       const char *name;
>> +
>> +       name = class->name;
>> +       if (!name)
>> +               name = __get_key_name(class->key, str);
>> +
>> +       return printk("%s", name);
>> +}
>> +
>>  static void print_lock_name(struct lock_class *class)
>>  {
>>        char str[KSYM_NAME_LEN], usage[LOCK_USAGE_CHARS];
>> @@ -1325,6 +1337,62 @@ print_shortest_lock_dependencies(struct lock_list *leaf,
>>        return;
>>  }
>>
>> +static void
>> +print_irq_lock_scenario(struct lock_list *safe_entry,
>> +                       struct lock_list *unsafe_entry,
>> +                       struct held_lock *prev,
>> +                       struct held_lock *next)
>> +{
>> +       struct lock_class *safe_class = safe_entry->class;
>> +       struct lock_class *unsafe_class = unsafe_entry->class;
>> +       struct lock_class *middle_class = hlock_class(prev);
>> +
>> +       if (middle_class == safe_class)
>> +               middle_class = hlock_class(next);
>> +
>> +       /*
>> +        * A direct locking problem where unsafe_class lock is taken
>> +        * directly by safe_class lock, then all we need to show
>> +        * is the deadlock scenario, as it is obvious that the
>> +        * unsafe lock is taken under the safe lock.
>> +        *
>> +        * But if there is a chain instead, where the safe lock takes
>> +        * an intermediate lock (middle_class) where this lock is
>> +        * not the same as the safe lock, then the lock chain is
>> +        * used to describe the problem. Otherwise we would need
>> +        * to show a different CPU case for each link in the chain
>> +        * from the safe_class lock to the unsafe_class lock.
>> +        */
>> +       if (middle_class != unsafe_class) {
>> +               printk("Chain exists of:\n  ");
>> +               __print_lock_name(safe_class);
>> +               printk(" --> ");
>> +               __print_lock_name(middle_class);
>> +               printk(" --> ");
>> +               __print_lock_name(unsafe_class);
>> +               printk("\n\n");
>> +       }
>> +
>> +       printk(" Possible interrupt unsafe locking scenario:\n\n");
>> +       printk("       CPU0                    CPU1\n");
>> +       printk("       ----                    ----\n");
>> +       printk("  lock(");
>> +       __print_lock_name(unsafe_class);
>> +       printk(");\n");
>> +       printk("                               local_irq_disable();\n");
>> +       printk("                               lock(");
>> +       __print_lock_name(safe_class);
>> +       printk(");\n");
>> +       printk("                               lock(");
>> +       __print_lock_name(middle_class);
>> +       printk(");\n");
>> +       printk("  <Interrupt>\n");
>> +       printk("    lock(");
>> +       __print_lock_name(safe_class);
>> +       printk(");\n");
>> +       printk("\n *** DEADLOCK ***\n\n");
>> +}
>> +
>>  static int
>>  print_bad_irq_dependency(struct task_struct *curr,
>>                         struct lock_list *prev_root,
>> @@ -1376,6 +1444,8 @@ print_bad_irq_dependency(struct task_struct *curr,
>>        print_stack_trace(forwards_entry->class->usage_traces + bit2, 1);
>>
>>        printk("\nother info that might help us debug this:\n\n");
>> +       print_irq_lock_scenario(backwards_entry, forwards_entry, prev, next);
>> +
>>        lockdep_print_held_locks(curr);
>>
>>        printk("\nthe dependencies between %s-irq-safe lock", irqclass);
>> --
>> 1.7.2.3
>>
>>
>> --
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>
>
>
> --
> Only stand for myself
>



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