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authorDmitry Vyukov <dvyukov@google.com>2016-02-04 14:40:40 +0100
committerIngo Molnar <mingo@kernel.org>2016-02-09 11:06:08 +0100
commit8a5fd56431fe1682e870bd6ab0c276e74befbeb9 (patch)
treebc2047bcdb5f7a29656deeaee113b8223b5246db /kernel
parent765bdb406de4b6132e349c5d4e077866536a9cc0 (diff)
downloadlinux-8a5fd56431fe1682e870bd6ab0c276e74befbeb9.tar.bz2
locking/lockdep: Fix stack trace caching logic
check_prev_add() caches saved stack trace in static trace variable to avoid duplicate save_trace() calls in dependencies involving trylocks. But that caching logic contains a bug. We may not save trace on first iteration due to early return from check_prev_add(). Then on the second iteration when we actually need the trace we don't save it because we think that we've already saved it. Let check_prev_add() itself control when stack is saved. There is another bug. Trace variable is protected by graph lock. But we can temporary release graph lock during printing. Fix this by invalidating cached stack trace when we release graph lock. Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: glider@google.com Cc: kcc@google.com Cc: peter@hurleysoftware.com Cc: sasha.levin@oracle.com Link: http://lkml.kernel.org/r/1454593240-121647-1-git-send-email-dvyukov@google.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/locking/lockdep.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 60ace56618f6..c7710e4092ef 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1822,7 +1822,7 @@ check_deadlock(struct task_struct *curr, struct held_lock *next,
*/
static int
check_prev_add(struct task_struct *curr, struct held_lock *prev,
- struct held_lock *next, int distance, int trylock_loop)
+ struct held_lock *next, int distance, int *stack_saved)
{
struct lock_list *entry;
int ret;
@@ -1883,8 +1883,11 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
}
}
- if (!trylock_loop && !save_trace(&trace))
- return 0;
+ if (!*stack_saved) {
+ if (!save_trace(&trace))
+ return 0;
+ *stack_saved = 1;
+ }
/*
* Ok, all validations passed, add the new lock
@@ -1907,6 +1910,8 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
* Debugging printouts:
*/
if (verbose(hlock_class(prev)) || verbose(hlock_class(next))) {
+ /* We drop graph lock, so another thread can overwrite trace. */
+ *stack_saved = 0;
graph_unlock();
printk("\n new dependency: ");
print_lock_name(hlock_class(prev));
@@ -1929,7 +1934,7 @@ static int
check_prevs_add(struct task_struct *curr, struct held_lock *next)
{
int depth = curr->lockdep_depth;
- int trylock_loop = 0;
+ int stack_saved = 0;
struct held_lock *hlock;
/*
@@ -1956,7 +1961,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
*/
if (hlock->read != 2 && hlock->check) {
if (!check_prev_add(curr, hlock, next,
- distance, trylock_loop))
+ distance, &stack_saved))
return 0;
/*
* Stop after the first non-trylock entry,
@@ -1979,7 +1984,6 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
if (curr->held_locks[depth].irq_context !=
curr->held_locks[depth-1].irq_context)
break;
- trylock_loop = 1;
}
return 1;
out_bug: