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Message-ID: <BANLkTimdMP52JCWCJp9Qfz=kWDMYWdQqgg@mail.gmail.com>
Date: Thu, 21 Apr 2011 14:43:22 +0800
From: Yong Zhang <yong.zhang0@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
"H. Peter Anvin" <hpa@...or.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/7] lockdep: Print a nice description of an irq locking issue
On Thu, Apr 21, 2011 at 9:41 AM, Steven Rostedt <rostedt@...dmis.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 ***
But this is not a real deadlock, right? Or maybe you can teach me :)
I just assume your scenario should show a more real one, But for
a possible irq-dependence deadlock, it seems not easy to find out.
Thanks,
Yong
>
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.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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