mfd: syscon: Fix race in device_node_get_regmap()

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() such as
kzalloc() and of_clk_get() may sleep.

Fixes: bdb0066df96e ("mfd: syscon: Decouple syscon interface from platform devices")
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Tested-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Tested-by: Will McVicker <willmcvicker@google.com>
Tested-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Link: https://lore.kernel.org/r/20241217-syscon-fixes-v2-1-4f56d750541d@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>

diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
index 3e1d699ba9340f8135dfdeae6feca474980cc48d..72f20de9652da2d7bad12e4bc2c43ac0c9a97f76 100644 (file)
--- 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;
 }