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authorPeter Zijlstra <peterz@infradead.org>2017-10-04 11:13:37 +0200
committerIngo Molnar <mingo@kernel.org>2017-10-10 10:04:28 +0200
commit8b405d5c5d0996d3d16f70c42744a0500f5b6ec3 (patch)
tree3cac3b08d64fc4cda870579eaef748f955ec2c08
parent529a86e063e9ff625c4ff247d8aa17d8072444fb (diff)
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: ce07a9415f26 ("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: Josh Poimboeuf <jpoimboe@redhat.com> Reported-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Peter 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: ce07a9415f26 ("locking/lockdep: Make check_prev_add() able to handle external stack_trace") Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/locking/lockdep.c48
1 files changed, 20 insertions, 28 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 44c8d0d17170..e36e652d996f 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -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.
@@ -2018,18 +2017,11 @@ 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
* own direct dependencies already, so this