linux-kernel - [tip:locking/core] locking/lockdep: Adjust lock usage bit character checks

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Date:   Mon, 3 Jun 2019 06:07:50 -0700
From:   tip-bot for Yuyang Du <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, duyuyang@...il.com, mingo@...nel.org,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: [tip:locking/core] locking/lockdep: Adjust lock usage bit character
 checks

Commit-ID:  c52478f4f38ace598475413a08dba9b9fd827eaf
Gitweb:     https://git.kernel.org/tip/c52478f4f38ace598475413a08dba9b9fd827eaf
Author:     Yuyang Du <duyuyang@...il.com>
AuthorDate: Mon, 6 May 2019 16:19:19 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 3 Jun 2019 11:55:35 +0200

locking/lockdep: Adjust lock usage bit character checks

The lock usage bit characters are defined and determined with tricks.
Add some explanation to make it a bit clearer, then adjust the logic to
check the usage, which optimizes the code a bit.

No functional change.

Signed-off-by: Yuyang Du <duyuyang@...il.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: bvanassche@....org
Cc: frederic@...nel.org
Cc: ming.lei@...hat.com
Cc: will.deacon@....com
Link: https://lkml.kernel.org/r/20190506081939.74287-4-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/locking/lockdep.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 109b56267c8f..a033df00fd1d 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -500,15 +500,26 @@ static inline unsigned long lock_flag(enum lock_usage_bit bit)
 
 static char get_usage_char(struct lock_class *class, enum lock_usage_bit bit)
 {
+	/*
+	 * The usage character defaults to '.' (i.e., irqs disabled and not in
+	 * irq context), which is the safest usage category.
+	 */
 	char c = '.';
 
-	if (class->usage_mask & lock_flag(bit + LOCK_USAGE_DIR_MASK))
+	/*
+	 * The order of the following usage checks matters, which will
+	 * result in the outcome character as follows:
+	 *
+	 * - '+': irq is enabled and not in irq context
+	 * - '-': in irq context and irq is disabled
+	 * - '?': in irq context and irq is enabled
+	 */
+	if (class->usage_mask & lock_flag(bit + LOCK_USAGE_DIR_MASK)) {
 		c = '+';
-	if (class->usage_mask & lock_flag(bit)) {
-		c = '-';
-		if (class->usage_mask & lock_flag(bit + LOCK_USAGE_DIR_MASK))
+		if (class->usage_mask & lock_flag(bit))
 			c = '?';
-	}
+	} else if (class->usage_mask & lock_flag(bit))
+		c = '-';
 
 	return c;
 }