Messages in this thread Patch in this message | | | Date | Thu, 21 Apr 2011 15:02:05 +0800 | Subject | Re: [PATCH 1/7] lockdep: Print a nice description of an irq locking issue | From | Yong Zhang <> |
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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(); 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 > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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