Commit 8b405d5c authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

locking/lockdep: Fix stacktrace mess 



There is some complication between check_prevs_add() and
check_prev_add() wrt. saving stack traces. The problem is that we want
to be frugal with saving stack traces, since it consumes static
resources.

We'll only know in check_prev_add() if we need the trace, but we can
call into it multiple times. So we want to do on-demand and re-use.

A further complication is that check_prev_add() can drop graph_lock
and mess with our static resources.

In any case, the current state; after commit:

  ce07a941 ("locking/lockdep: Make check_prev_add() able to handle external stack_trace")

is that we'll assume the trace contains valid data once
check_prev_add() returns '2'. However, as noted by Josh, this is
false, check_prev_add() can return '2' before having saved a trace,
this then result in the possibility of using uninitialized data.
Testing, as reported by Wu, shows a NULL deref.

So simplify.

Since the graph_lock() thing is a debug path that hasn't
really been used in a long while, take it out back and avoid the
head-ache.

Further initialize the stack_trace to a known 'empty' state; as long
as nr_entries == 0, nothing should deref entries. We can then use the
'entries == NULL' test for a valid trace / on-demand saving.

Analyzed-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Reported-by: default avatarFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: ce07a941 ("locking/lockdep: Make check_prev_add() able to handle external stack_trace")
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 529a86e0

kernel/locking/lockdep.c

+20 −28
Original line number Diff line number Diff line
@@ -1873,10 +1873,10 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, 
	       struct held_lock *next, int distance, struct stack_trace *trace,

	       int (*save)(struct stack_trace *trace))

{

	struct lock_list *uninitialized_var(target_entry);

	struct lock_list *entry;

	int ret;

	struct lock_list this;

	struct lock_list *uninitialized_var(target_entry);

	int ret;



	/*

	 * Prove that the new <prev> -> <next> dependency would not
@@ -1890,8 +1890,17 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, 
	this.class = hlock_class(next);

	this.parent = NULL;

	ret = check_noncircular(&this, hlock_class(prev), &target_entry);

	if (unlikely(!ret))

	if (unlikely(!ret)) {

		if (!trace->entries) {

			/*

			 * If @save fails here, the printing might trigger

			 * a WARN but because of the !nr_entries it should

			 * not do bad things.

			 */

			save(trace);

		}

		return print_circular_bug(&this, target_entry, next, prev, trace);

	}

	else if (unlikely(ret < 0))

		return print_bfs_bug(ret);
@@ -1938,7 +1947,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, 
		return print_bfs_bug(ret);





	if (save && !save(trace))

	if (!trace->entries && !save(trace))

		return 0;



	/*
@@ -1958,20 +1967,6 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, 
	if (!ret)

		return 0;



	/*

	 * Debugging printouts:

	 */

	if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {

		graph_unlock();

		printk("\n new dependency: ");

		print_lock_name(hlock_class(prev));

		printk(KERN_CONT " => ");

		print_lock_name(hlock_class(next));

		printk(KERN_CONT "\n");

		dump_stack();

		if (!graph_lock())

			return 0;

	}

	return 2;

}
@@ -1986,8 +1981,12 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) 
{

	int depth = curr->lockdep_depth;

	struct held_lock *hlock;

	struct stack_trace trace;

	int (*save)(struct stack_trace *trace) = save_trace;

	struct stack_trace trace = {

		.nr_entries = 0,

		.max_entries = 0,

		.entries = NULL,

		.skip = 0,

	};



	/*

	 * Debugging checks.
@@ -2018,17 +2017,10 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) 
			 */

			if (hlock->read != 2 && hlock->check) {

				int ret = check_prev_add(curr, hlock, next,

							 distance, &trace, save);

							 distance, &trace, save_trace);

				if (!ret)

					return 0;



				/*

				 * Stop saving stack_trace if save_trace() was

				 * called at least once:

				 */

				if (save && ret == 2)

					save = NULL;



				/*

				 * Stop after the first non-trylock entry,

				 * as non-trylock entries have added their

CRA Git | Maintained and supported by SUSTech CRA and CCSE