[PATCH 1/3] mfd: syscon: Fix race in device_node_get_regmap()

Rob Herring (Arm)
2024-12-11T20:57:30Z

It is possible for multiple, simultaneous callers calling
device_node_get_regmap() with the same node to fail to find an entry in
the syscon_list. There is a period of time while the first caller is
calling of_syscon_register() that subsequent callers also fail to find
an entry in the syscon_list and then call of_syscon_register() a second
time.

Fix this by keeping the lock held until after of_syscon_register()
completes and adds the node to syscon_list. Convert the spinlock to a
mutex as many of the functions called in of_syscon_register() may sleep.

Fixes: bdb0066df96e ("mfd: syscon: Decouple syscon interface from platform devices")
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
---
drivers/mfd/syscon.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
index 3e1d699ba934..72f20de9652d 100644
--- a/drivers/mfd/syscon.c
+++ b/drivers/mfd/syscon.c
@@ -15,6 +15,7 @@
#include <linux/io.h>
#include <linux/init.h>
#include <linux/list.h>
+#include <linux/mutex.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_platform.h>
@@ -27,7 +28,7 @@

static struct platform_driver syscon_driver;

-static DEFINE_SPINLOCK(syscon_list_slock);
+static DEFINE_MUTEX(syscon_list_lock);
static LIST_HEAD(syscon_list);

struct syscon {
@@ -54,6 +55,8 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
struct resource res;
struct reset_control *reset;

+ WARN_ON(!mutex_is_locked(&syscon_list_lock));
+
struct syscon *syscon __free(kfree) = kzalloc(sizeof(*syscon), GFP_KERNEL);
if (!syscon)
return ERR_PTR(-ENOMEM);
@@ -146,9 +149,7 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
syscon->regmap = regmap;
syscon->np = np;

- spin_lock(&syscon_list_slock);
list_add_tail(&syscon->list, &syscon_list);
- spin_unlock(&syscon_list_slock);

return_ptr(syscon);

@@ -169,7 +170,7 @@ static struct regmap *device_node_get_regmap(struct device_node *np,
{
struct syscon *entry, *syscon = NULL;

- spin_lock(&syscon_list_slock);
+ mutex_lock(&syscon_list_lock);

list_for_each_entry(entry, &syscon_list, list)
if (entry->np == np) {
@@ -177,11 +178,11 @@ static struct regmap *device_node_get_regmap(struct device_node *np,
break;
}

- spin_unlock(&syscon_list_slock);
-
if (!syscon)
syscon = of_syscon_register(np, check_res);

+ mutex_unlock(&syscon_list_lock);
+
if (IS_ERR(syscon))
return ERR_CAST(syscon);

@@ -212,7 +213,7 @@ int of_syscon_register_regmap(struct device_node *np, struct regmap *regmap)
return -ENOMEM;

/* check if syscon entry already exists */
- spin_lock(&syscon_list_slock);
+ mutex_lock(&syscon_list_lock);

list_for_each_entry(entry, &syscon_list, list)
if (entry->np == np) {
@@ -225,12 +226,12 @@ int of_syscon_register_regmap(struct device_node *np, struct regmap *regmap)

/* register the regmap in syscon list */
list_add_tail(&syscon->list, &syscon_list);
- spin_unlock(&syscon_list_slock);
+ mutex_unlock(&syscon_list_lock);

return 0;

err_unlock:
- spin_unlock(&syscon_list_slock);
+ mutex_unlock(&syscon_list_lock);
kfree(syscon);
return ret;
}

--
2.45.2