[PATCH] platform/x86: ISST: Fix possible circular locking dependency detected

From: Srinivas Pandruvada
Date: Tue Jan 11 2022 - 21:25:28 EST

As reported:

[ 256.104522] ======================================================
[ 256.113783] WARNING: possible circular locking dependency detected
[ 256.120093] 5.16.0-rc6-yocto-standard+ #99 Not tainted
[ 256.125362] ------------------------------------------------------
[ 256.131673] intel-speed-sel/844 is trying to acquire lock:
[ 256.137290] ffffffffc036f0d0 (punit_misc_dev_lock){+.+.}-{3:3}, at: isst_if_open+0x18/0x90 [isst_if_common]
[ 256.147171]
[ 256.147171] but task is already holding lock:
[ 256.153135] ffffffff8ee7cb50 (misc_mtx){+.+.}-{3:3}, at: misc_open+0x2a/0x170
[ 256.160407]
[ 256.160407] which lock already depends on the new lock.
[ 256.160407]
[ 256.168712]
[ 256.168712] the existing dependency chain (in reverse order) is:
[ 256.176327]
[ 256.176327] -> #1 (misc_mtx){+.+.}-{3:3}:
[ 256.181946] lock_acquire+0x1e6/0x330
[ 256.186265] __mutex_lock+0x9b/0x9b0
[ 256.190497] mutex_lock_nested+0x1b/0x20
[ 256.195075] misc_register+0x32/0x1a0
[ 256.199390] isst_if_cdev_register+0x65/0x180 [isst_if_common]
[ 256.205878] isst_if_probe+0x144/0x16e [isst_if_mmio]
...
[ 256.241976]
[ 256.241976] -> #0 (punit_misc_dev_lock){+.+.}-{3:3}:
[ 256.248552] validate_chain+0xbc6/0x1750
[ 256.253131] __lock_acquire+0x88c/0xc10
[ 256.257618] lock_acquire+0x1e6/0x330
[ 256.261933] __mutex_lock+0x9b/0x9b0
[ 256.266165] mutex_lock_nested+0x1b/0x20
[ 256.270739] isst_if_open+0x18/0x90 [isst_if_common]
[ 256.276356] misc_open+0x100/0x170
[ 256.280409] chrdev_open+0xa5/0x1e0
...

The call sequence suggested that misc_device /dev file can be opened
before misc device is yet to be registered, which is done only once.

Here punit_misc_dev_lock was used as common lock, to protect the
registration by multiple ISST HW drivers, one time setup, prevent
duplicate registry of misc device and prevent load/unload when device
is open.

We can split into locks:
- One which just prevent duplicate call to misc_register() and one
time setup. Also never call again if the misc_register() failed or
required one time setup is failed. This lock is not shared with
any misc device callbacks.

- The other lock protects registry, load and unload of HW drivers.

Sequence in isst_if_cdev_register()
- Register callbacks under punit_misc_dev_open_lock
- Call isst_misc_reg() which registers misc_device on the first
registry which is under punit_misc_dev_reg_lock, which is not
shared with callbacks.

Sequence in isst_if_cdev_unregister
Just opposite of isst_if_cdev_register

Reported-and-tested-by: Liwei Song <liwei.song@xxxxxxxxxxxxx>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
---
.../intel/speed_select_if/isst_if_common.c | 97 ++++++++++++-------
1 file changed, 63 insertions(+), 34 deletions(-)

diff --git a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
index c9a85eb2e860..e8424e70d81d 100644
--- a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
+++ b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
@@ -596,7 +596,10 @@ static long isst_if_def_ioctl(struct file *file, unsigned int cmd,
return ret;
}

-static DEFINE_MUTEX(punit_misc_dev_lock);
+/* Lock to prevent module registration when already opened by user space */
+static DEFINE_MUTEX(punit_misc_dev_open_lock);
+/* Lock to allow one share misc device for all ISST interace */
+static DEFINE_MUTEX(punit_misc_dev_reg_lock);
static int misc_usage_count;
static int misc_device_ret;
static int misc_device_open;
@@ -606,7 +609,7 @@ static int isst_if_open(struct inode *inode, struct file *file)
int i, ret = 0;

/* Fail open, if a module is going away */
- mutex_lock(&punit_misc_dev_lock);
+ mutex_lock(&punit_misc_dev_open_lock);
for (i = 0; i < ISST_IF_DEV_MAX; ++i) {
struct isst_if_cmd_cb *cb = &punit_callbacks[i];

@@ -628,7 +631,7 @@ static int isst_if_open(struct inode *inode, struct file *file)
} else {
misc_device_open++;
}
- mutex_unlock(&punit_misc_dev_lock);
+ mutex_unlock(&punit_misc_dev_open_lock);

return ret;
}
@@ -637,7 +640,7 @@ static int isst_if_relase(struct inode *inode, struct file *f)
{
int i;

- mutex_lock(&punit_misc_dev_lock);
+ mutex_lock(&punit_misc_dev_open_lock);
misc_device_open--;
for (i = 0; i < ISST_IF_DEV_MAX; ++i) {
struct isst_if_cmd_cb *cb = &punit_callbacks[i];
@@ -645,7 +648,7 @@ static int isst_if_relase(struct inode *inode, struct file *f)
if (cb->registered)
module_put(cb->owner);
}
- mutex_unlock(&punit_misc_dev_lock);
+ mutex_unlock(&punit_misc_dev_open_lock);

return 0;
}
@@ -662,6 +665,43 @@ static struct miscdevice isst_if_char_driver = {
.fops = &isst_if_char_driver_ops,
};

+static int isst_misc_reg(void)
+{
+ mutex_lock(&punit_misc_dev_reg_lock);
+ if (misc_device_ret)
+ goto unlock_exit;
+
+ if (!misc_usage_count) {
+ misc_device_ret = isst_if_cpu_info_init();
+ if (misc_device_ret)
+ goto unlock_exit;
+
+ misc_device_ret = misc_register(&isst_if_char_driver);
+ if (misc_device_ret) {
+ isst_if_cpu_info_exit();
+ goto unlock_exit;
+ }
+ }
+ misc_usage_count++;
+
+unlock_exit:
+ mutex_unlock(&punit_misc_dev_reg_lock);
+
+ return misc_device_ret;
+}
+
+static void isst_misc_unreg(void)
+{
+ mutex_lock(&punit_misc_dev_reg_lock);
+ if (misc_usage_count)
+ misc_usage_count--;
+ if (!misc_usage_count && !misc_device_ret) {
+ misc_deregister(&isst_if_char_driver);
+ isst_if_cpu_info_exit();
+ }
+ mutex_unlock(&punit_misc_dev_reg_lock);
+}
+
/**
* isst_if_cdev_register() - Register callback for IOCTL
* @device_type: The device type this callback handling.
@@ -679,38 +719,31 @@ static struct miscdevice isst_if_char_driver = {
*/
int isst_if_cdev_register(int device_type, struct isst_if_cmd_cb *cb)
{
- if (misc_device_ret)
- return misc_device_ret;
+ int ret;

if (device_type >= ISST_IF_DEV_MAX)
return -EINVAL;

- mutex_lock(&punit_misc_dev_lock);
+ mutex_lock(&punit_misc_dev_open_lock);
+ /* Device is already open, we don't want to add new callbacks */
if (misc_device_open) {
- mutex_unlock(&punit_misc_dev_lock);
+ mutex_unlock(&punit_misc_dev_open_lock);
return -EAGAIN;
}
- if (!misc_usage_count) {
- int ret;
-
- misc_device_ret = misc_register(&isst_if_char_driver);
- if (misc_device_ret)
- goto unlock_exit;
-
- ret = isst_if_cpu_info_init();
- if (ret) {
- misc_deregister(&isst_if_char_driver);
- misc_device_ret = ret;
- goto unlock_exit;
- }
- }
memcpy(&punit_callbacks[device_type], cb, sizeof(*cb));
punit_callbacks[device_type].registered = 1;
- misc_usage_count++;
-unlock_exit:
- mutex_unlock(&punit_misc_dev_lock);
+ mutex_unlock(&punit_misc_dev_open_lock);

- return misc_device_ret;
+ ret = isst_misc_reg();
+ if (ret) {
+ /*
+ * No need of mutex as the misc device register failed
+ * as no one can open device yet. Hence no contention.
+ */
+ punit_callbacks[device_type].registered = 0;
+ return ret;
+ }
+ return 0;
}
EXPORT_SYMBOL_GPL(isst_if_cdev_register);

@@ -725,16 +758,12 @@ EXPORT_SYMBOL_GPL(isst_if_cdev_register);
*/
void isst_if_cdev_unregister(int device_type)
{
- mutex_lock(&punit_misc_dev_lock);
- misc_usage_count--;
+ isst_misc_unreg();
+ mutex_lock(&punit_misc_dev_open_lock);
punit_callbacks[device_type].registered = 0;
if (device_type == ISST_IF_DEV_MBOX)
isst_delete_hash();
- if (!misc_usage_count && !misc_device_ret) {
- misc_deregister(&isst_if_char_driver);
- isst_if_cpu_info_exit();
- }
- mutex_unlock(&punit_misc_dev_lock);
+ mutex_unlock(&punit_misc_dev_open_lock);
}
EXPORT_SYMBOL_GPL(isst_if_cdev_unregister);

--
2.25.1