linux-kernel - [PATCH 33/36] tty/vt: consolemap: change refcount only if needed in con_do_clear

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Message-Id: <20220607104946.18710-33-jslaby@suse.cz>
Date:   Tue,  7 Jun 2022 12:49:43 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     gregkh@...uxfoundation.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 33/36] tty/vt: consolemap: change refcount only if needed in con_do_clear_unimap()

con_do_clear_unimap() currently decreases and increases refcount of old
dictionary in a back and forth fashion. This makes the code really hard
to follow. Decrease the refcount only if everything went well and we
really allocated a new one and decoupled from the old dictionary.

I sincerelly hope I did not make a mistake in this (ill) logic.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/tty/vt/consolemap.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/vt/consolemap.c b/drivers/tty/vt/consolemap.c
index 01b7e49f1f91..4d8efe74315c 100644
--- a/drivers/tty/vt/consolemap.c
+++ b/drivers/tty/vt/consolemap.c
@@ -535,22 +535,23 @@ static int con_do_clear_unimap(struct vc_data *vc)
 {
 	struct uni_pagedict *old = *vc->vc_uni_pagedir_loc;
 
-	if (!old || --old->refcount) {
+	if (!old || old->refcount > 1) {
 		struct uni_pagedict *new = kzalloc(sizeof(*new), GFP_KERNEL);
-		if (!new) {
-			if (old)
-				old->refcount++;
+		if (!new)
 			return -ENOMEM;
-		}
+
 		new->refcount = 1;
 		*vc->vc_uni_pagedir_loc = new;
+
+		if (old)
+			old->refcount--;
 	} else {
 		if (old == dflt)
 			dflt = NULL;
-		old->refcount++;
 		old->sum = 0;
 		con_release_unimap(old);
 	}
+
 	return 0;
 }
 
-- 
2.36.1