linux-kernel - lockdep tracing and using of printk return value ?

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Message-ID: <335067f871a85db5f24650a3dff96f19727bed50.camel@perches.com>
Date:   Tue, 19 May 2020 05:41:47 -0700
From:   Joe Perches <joe@...ches.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>
Subject: lockdep tracing and using of printk return value ?

Except for some ancient code in drivers/scsi, this code
may be the only kernel use of the printk return value.

Code that uses the printk return value in
kernel/locking/lockdep.c is odd because the printk
return length includes both the length of a KERN_<LEVEL>
prefix and the newline.  depth also seems double counted.

Perhaps there's a better way to calculate this?

Maybe:
---
 kernel/locking/lockdep.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 2fadc2635946..265227edc550 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1960,11 +1960,9 @@ static void print_lock_class_header(struct lock_class *class, int depth)
 
 	for (bit = 0; bit < LOCK_USAGE_STATES; bit++) {
 		if (class->usage_mask & (1 << bit)) {
-			int len = depth;
-
-			len += printk("%*s   %s", depth, "", usage_str[bit]);
-			len += printk(KERN_CONT " at:\n");
-			print_lock_trace(class->usage_traces[bit], len);
+			printk("%*s   %s at:\n", depth, "", usage_str[bit]);
+			print_lock_trace(class->usage_traces[bit],
+					 depth + 3 + strlen(usage_str[bit]);
 		}
 	}
 	printk("%*s }\n", depth, "");