linux-kernel - [tip: locking/urgent] lockdep: Fix nr_unused

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Message-ID: <160414383158.397.3025016969633820018.tip-bot2@tip-bot2>
Date:   Sat, 31 Oct 2020 11:30:31 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: locking/urgent] lockdep: Fix nr_unused_locks accounting

The following commit has been merged into the locking/urgent branch of tip:

Commit-ID:     1a39340865ce505a029b37aeb47a3e4c8db5f6c6
Gitweb:        https://git.kernel.org/tip/1a39340865ce505a029b37aeb47a3e4c8db5f6c6
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 27 Oct 2020 13:48:34 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Fri, 30 Oct 2020 17:07:18 +01:00

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@...is-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Chris Wilson <chris@...is-wilson.co.uk>
Link: https://lkml.kernel.org/r/20201027124834.GL2628@hirez.programming.kicks-ass.net
---
 kernel/locking/lockdep.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 1102849..b71ad8d 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -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: