Commit c8a25005 authored Apr 17, 2009 by Peter Zijlstra Committed by Ingo Molnar Apr 17, 2009

lockdep: more robust lockdep_map init sequence



Steven Rostedt reported:

> OK, I think I figured this bug out. This is a lockdep issue with respect
> to tracepoints.
>
> The trace points in lockdep are called all the time. Outside the lockdep
> logic. But if lockdep were to trigger an error / warning (which this run
> did) we might be in trouble. For new locks, like the dentry->d_lock, that
> are created, they will not get a name:
>
> void lockdep_init_map(struct lockdep_map *lock, const char *name,
>                       struct lock_class_key *key, int subclass)
> {
>         if (unlikely(!debug_locks))
>                 return;
>
> When a problem is found by lockdep, debug_locks becomes false. Thus we
> stop allocating names for locks. This dentry->d_lock I had, now has no
> name. Worse yet, I have CONFIG_DEBUG_VM set, that scrambles non
> initialized memory. Thus, when the trace point was hit, it had junk for
> the lock->name, and the machine crashed.

Ah, nice catch. I think we should put at least the name in regardless.

Ensure we at least initialize the trivial entries of the depmap so that
they can be relied upon, even when lockdep itself decided to pack up and
go home.

[ Impact: fix lock tracing after lockdep warnings. ]

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1239954049.23397.4156.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 79d381c9

kernel/lockdep.c

+14 −8

Original line number	Diff line number	Diff line
		@@ -2490,13 +2490,20 @@ static int mark_lock(struct task_struct curr, struct held_lock this,
		void lockdep_init_map(struct lockdep_map lock, const char name,
		struct lock_class_key *key, int subclass)
		{
		if (unlikely(!debug_locks))
		lock->class_cache = NULL;
		#ifdef CONFIG_LOCK_STAT
		lock->cpu = raw_smp_processor_id();
		#endif

		if (DEBUG_LOCKS_WARN_ON(!name)) {
		lock->name = "NULL";
		return;
		}

		lock->name = name;

		if (DEBUG_LOCKS_WARN_ON(!key))
		return;
		if (DEBUG_LOCKS_WARN_ON(!name))
		return;
		/*
		* Sanity check, the lock-class key must be persistent:
		*/
		@@ -2505,12 +2512,11 @@ void lockdep_init_map(struct lockdep_map lock, const char name,
		DEBUG_LOCKS_WARN_ON(1);
		return;
		}
		lock->name = name;
		lock->key = key;
		lock->class_cache = NULL;
		#ifdef CONFIG_LOCK_STAT
		lock->cpu = raw_smp_processor_id();
		#endif

		if (unlikely(!debug_locks))
		return;

		if (subclass)
		register_lock_class(lock, subclass, 1);
		}

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