linux-kernel - Re: [PATCH 1/2] lockdep: add lockdep_assert_not

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Message-ID: <20210215104402.GC4507@worktop.programming.kicks-ass.net>
Date:   Mon, 15 Feb 2021 11:44:02 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     mingo@...hat.com, will@...nel.org, kvalo@...eaurora.org,
        davem@...emloft.net, kuba@...nel.org, ath10k@...ts.infradead.org,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] lockdep: add lockdep_assert_not_held()

On Sun, Feb 14, 2021 at 06:53:01PM +0100, Peter Zijlstra wrote:
> On Fri, Feb 12, 2021 at 04:28:42PM -0700, Shuah Khan wrote:
> 
> > +#define lockdep_assert_not_held(l)	do {			\
> > +		WARN_ON(debug_locks && lockdep_is_held(l));	\
> > +	} while (0)
> > +
> 
> This thing isn't as straight forward as you might think, but it'll
> mostly work.
> 
> Notably this thing will misfire when lockdep_off() is employed. It
> certainyl needs a comment to explain the subtleties.

I think something like so will work, but please double check.

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index b9e9adec73e8..c8b0d292bf8e 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -294,11 +294,15 @@ extern void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie);
 
 #define lockdep_depth(tsk)	(debug_locks ? (tsk)->lockdep_depth : 0)
 
-#define lockdep_assert_held(l)	do {				\
-		WARN_ON(debug_locks && !lockdep_is_held(l));	\
+#define lockdep_assert_held(l)	do {					\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 0));	\
 	} while (0)
 
-#define lockdep_assert_held_write(l)	do {			\
+#define lockdep_assert_not_held(l)	do {				\
+		WARN_ON(debug_locks && lockdep_is_held(l) == 1));	\
+	} while (0)
+
+#define lockdep_assert_held_write(l)	do {				\
 		WARN_ON(debug_locks && !lockdep_is_held_type(l, 0));	\
 	} while (0)
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c1418b47f625..983ba206f7b2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -5467,7 +5467,7 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
 	int ret = 0;
 
 	if (unlikely(!lockdep_enabled()))
-		return 1; /* avoid false negative lockdep_assert_held() */
+		return -1; /* avoid false negative lockdep_assert_held() */
 
 	raw_local_irq_save(flags);
 	check_flags(flags);