linux-kernel - [PATCH v4 6/8] char: misc: Does not request module for miscdevice with dynamic minor

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Message-Id: <20250704-rfc_miscdev-v4-6-b48986112d6a@oss.qualcomm.com>
Date: Fri, 04 Jul 2025 21:26:04 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Arnd Bergmann <arnd@...db.de>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>, 
 Helge Deller <deller@....de>, "David S. Miller" <davem@...emloft.net>, 
 Andreas Larsson <andreas@...sler.com>
Cc: Thadeu Lima de Souza Cascardo <cascardo@...lia.com>, 
 Zijun Hu <zijun_hu@...oud.com>, linux-kernel@...r.kernel.org, 
 linux-parisc@...r.kernel.org, sparclinux@...r.kernel.org, 
 Zijun Hu <zijun.hu@....qualcomm.com>
Subject: [PATCH v4 6/8] char: misc: Does not request module for miscdevice
 with dynamic minor

From: Zijun Hu <zijun.hu@....qualcomm.com>

misc_open() may request module for miscdevice with dynamic minor
which is meaningless since macro MODULE_ALIAS_MISCDEV() is not
applicable for dynamic minor.

Fix by only requesting module for miscdevice with fixed minor.

Signed-off-by: Zijun Hu <zijun.hu@....qualcomm.com>
---
 drivers/char/misc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index 96ed343cf5c8509a09855020049a9af82a3ede95..a0aae0fc792666a7bdc0ba00da9dc02ff9cead42 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -132,7 +132,8 @@ static int misc_open(struct inode *inode, struct file *file)
 		break;
 	}

-	if (!new_fops) {
+	/* Only request module for fixed minor code */
+	if (!new_fops && minor < MISC_DYNAMIC_MINOR) {
 		mutex_unlock(&misc_mtx);
 		request_module("char-major-%d-%d", MISC_MAJOR, minor);
 		mutex_lock(&misc_mtx);
@@ -144,10 +145,11 @@ static int misc_open(struct inode *inode, struct file *file)
 			new_fops = fops_get(iter->fops);
 			break;
 		}
-		if (!new_fops)
-			goto fail;
 	}

+	if (!new_fops)
+		goto fail;
+
 	/*
 	 * Place the miscdevice in the file's
 	 * private_data so it can be used by the

-- 
2.34.1