linux-kernel - [PATCH 2/2] mtd: char: Get rid of Big MTD Lock

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Date:   Wed, 17 Feb 2021 22:18:45 +0100
From:   Alexander A Sverdlin <alexander.sverdlin@...ia.com>
To:     linux-mtd@...ts.infradead.org
Cc:     Alexander Sverdlin <alexander.sverdlin@...ia.com>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] mtd: char: Get rid of Big MTD Lock

From: Alexander Sverdlin <alexander.sverdlin@...ia.com>

Get rid of central chrdev MTD lock, which prevents simultaneous operations
on completely independent physical MTD chips. Replace it with newly
introduced per-master mutex.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>
---
 drivers/mtd/mtdchar.c   | 14 ++++++++------
 drivers/mtd/mtdcore.c   |  1 +
 include/linux/mtd/mtd.h |  1 +
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/mtdchar.c b/drivers/mtd/mtdchar.c
index f31390d..57c4a2f 100644
--- a/drivers/mtd/mtdchar.c
+++ b/drivers/mtd/mtdchar.c
@@ -27,8 +27,6 @@
 
 #include "mtdcore.h"
 
-static DEFINE_MUTEX(mtd_mutex);
-
 /*
  * Data structure to hold the pointer to the mtd device as well
  * as mode information of various use cases.
@@ -1020,11 +1018,14 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 
 static long mtdchar_unlocked_ioctl(struct file *file, u_int cmd, u_long arg)
 {
+	struct mtd_file_info *mfi = file->private_data;
+	struct mtd_info *mtd = mfi->mtd;
+	struct mtd_info *master = mtd_get_master(mtd);
 	int ret;
 
-	mutex_lock(&mtd_mutex);
+	mutex_lock(&master->master.chrdev_lock);
 	ret = mtdchar_ioctl(file, cmd, arg);
-	mutex_unlock(&mtd_mutex);
+	mutex_unlock(&master->master.chrdev_lock);
 
 	return ret;
 }
@@ -1045,10 +1046,11 @@ static long mtdchar_compat_ioctl(struct file *file, unsigned int cmd,
 {
 	struct mtd_file_info *mfi = file->private_data;
 	struct mtd_info *mtd = mfi->mtd;
+	struct mtd_info *master = mtd_get_master(mtd);
 	void __user *argp = compat_ptr(arg);
 	int ret = 0;
 
-	mutex_lock(&mtd_mutex);
+	mutex_lock(&master->master.chrdev_lock);
 
 	switch (cmd) {
 	case MEMWRITEOOB32:
@@ -1111,7 +1113,7 @@ static long mtdchar_compat_ioctl(struct file *file, unsigned int cmd,
 		ret = mtdchar_ioctl(file, cmd, (unsigned long)argp);
 	}
 
-	mutex_unlock(&mtd_mutex);
+	mutex_unlock(&master->master.chrdev_lock);
 
 	return ret;
 }
diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 2d6423d..0b09597 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -773,6 +773,7 @@ static void mtd_set_dev_defaults(struct mtd_info *mtd)
 
 	INIT_LIST_HEAD(&mtd->partitions);
 	mutex_init(&mtd->master.partitions_lock);
+	mutex_init(&mtd->master.chrdev_lock);
 }
 
 /**
diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index 157357e..ceabc2c 100644
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -229,6 +229,7 @@ struct mtd_part {
  */
 struct mtd_master {
 	struct mutex partitions_lock;
+	struct mutex chrdev_lock;
 	unsigned int suspended : 1;
 };
 
-- 
2.10.2