locking/lockdep: Fix stack trace caching logic (8a5fd564) · Commits · 戴 / test

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>

kernel/locking/lockdep.c

+10 −6

Original line number	Diff line number	Diff line
		@@ -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))
		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:

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