linux-kernel - [PATCH v2] lockdep: fix warning: print_lock

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Date:   Sun,  9 Jun 2019 17:09:33 -0700
From:   john.hubbard@...il.com
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH v2] lockdep: fix warning: print_lock_trace defined but not used

From: John Hubbard <jhubbard@...dia.com>

Commit 0d2cc3b34532 ("locking/lockdep: Move valid_state() inside
CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING") moved the only usage of
print_lock_trace() that was originally outside of the CONFIG_PROVE_LOCKING
case. It moved that usage into a different case: CONFIG_PROVE_LOCKING &&
CONFIG_TRACE_IRQFLAGS. That leaves things not symmetrical, and as a result,
the following warning fires on my build, when I have

!CONFIG_TRACE_IRQFLAGS && !CONFIG_PROVE_LOCKING

set:

kernel/locking/lockdep.c:2821:13: warning: ‘print_lock_trace’ defined
    but not used [-Wunused-function]

Fix this by annotating print_lock_trace() with "__maybe_unused".
Thanks to Paul E. McKenney for suggesting this less intrusive fix,
as compared to adding more ifdef noise.

Fixes: 0d2cc3b34532 ("locking/lockdep: Move valid_state() inside CONFIG_TRACE_IRQFLAGS && CONFIG_PROVE_LOCKING")

Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Will Deacon <will.deacon@....com>
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 kernel/locking/lockdep.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c47788fa85f9..2726dafdb29b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -2818,7 +2818,8 @@ static inline int validate_chain(struct task_struct *curr,
 	return 1;
 }
 
-static void print_lock_trace(struct lock_trace *trace, unsigned int spaces)
+static void __maybe_unused print_lock_trace(struct lock_trace *trace,
+					    unsigned int spaces)
 {
 }
 #endif
-- 
2.21.0