Commit 1a393408 authored Oct 27, 2020 by Peter Zijlstra

lockdep: Fix nr_unused_locks accounting



Chris reported that commit 24d5a3bffef1 ("lockdep: Fix
usage_traceoverflow") breaks the nr_unused_locks validation code
triggered by /proc/lockdep_stats.

By fully splitting LOCK_USED and LOCK_USED_READ it becomes a bad
indicator for accounting nr_unused_locks; simplyfy by using any first
bit.

Fixes: 24d5a3bffef1 ("lockdep: Fix usage_traceoverflow")
Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://lkml.kernel.org/r/20201027124834.GL2628@hirez.programming.kicks-ass.net

parent d48e3850

kernel/locking/lockdep.c

+4 −10

Original line number	Diff line number	Diff line
		@@ -4396,6 +4396,9 @@ static int mark_lock(struct task_struct curr, struct held_lock this,
		if (unlikely(hlock_class(this)->usage_mask & new_mask))
		goto unlock;

		if (!hlock_class(this)->usage_mask)
		debug_atomic_dec(nr_unused_locks);

		hlock_class(this)->usage_mask \|= new_mask;

		if (new_bit < LOCK_TRACE_STATES) {
		@@ -4403,19 +4406,10 @@ static int mark_lock(struct task_struct curr, struct held_lock this,
		return 0;
		}

		switch (new_bit) {
		case 0 ... LOCK_USED-1:
		if (new_bit < LOCK_USED) {
		ret = mark_lock_irq(curr, this, new_bit);
		if (!ret)
		return 0;
		break;

		case LOCK_USED:
		debug_atomic_dec(nr_unused_locks);
		break;

		default:
		break;
		}

		unlock:

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