Messages in this thread | | | Date | Thu, 21 Apr 2011 15:08:28 +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 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 >> >> >> -- >> 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/ >> > > > > -- > Only stand for myself >
-- Only stand for myself -- 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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