bus: mhi: ep: Change state_lock to mutex

state_lock, the spinlock type is meant to protect race against concurrent
MHI state transitions. In mhi_ep_set_m0_state(), while the state_lock is
being held, the channels are resumed in mhi_ep_resume_channels() if the
previous state was M3. This causes sleeping in atomic bug, since
mhi_ep_resume_channels() use mutex internally.

Since the state_lock is supposed to be held throughout the state change,
it is not ideal to drop the lock before calling mhi_ep_resume_channels().
So to fix this issue, let's change the type of state_lock to mutex. This
would also allow holding the lock throughout all state transitions thereby
avoiding any potential race.

Cc: <stable@vger.kernel.org> # 5.19
Fixes: e4b7b5f0 ("bus: mhi: ep: Add support for suspending and resuming channels")
Reported-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Jeffrey Hugo <quic_jhugo@quicinc.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

drivers/bus/mhi/ep/main.c

@@ -1001,11 +1001,11 @@ static void mhi_ep_reset_worker(struct work_struct *work)
 
 	mhi_ep_power_down(mhi_cntrl);
 
-	spin_lock_bh(&mhi_cntrl->state_lock);
+	mutex_lock(&mhi_cntrl->state_lock);
+
 	/* Reset MMIO to signal host that the MHI_RESET is completed in endpoint */
 	mhi_ep_mmio_reset(mhi_cntrl);
 	cur_state = mhi_cntrl->mhi_state;
-	spin_unlock_bh(&mhi_cntrl->state_lock);
 
 	/*
 	 * Only proceed further if the reset is due to SYS_ERR. The host will
@@ -1014,6 +1014,8 @@ static void mhi_ep_reset_worker(struct work_struct *work)
 	 */
 	if (cur_state == MHI_STATE_SYS_ERR)
 		mhi_ep_power_up(mhi_cntrl);
+
+	mutex_unlock(&mhi_cntrl->state_lock);
 }
 
 /*
@@ -1386,8 +1388,8 @@ int mhi_ep_register_controller(struct mhi_ep_cntrl *mhi_cntrl,
 
 	INIT_LIST_HEAD(&mhi_cntrl->st_transition_list);
 	INIT_LIST_HEAD(&mhi_cntrl->ch_db_list);
-	spin_lock_init(&mhi_cntrl->state_lock);
 	spin_lock_init(&mhi_cntrl->list_lock);
+	mutex_init(&mhi_cntrl->state_lock);
 	mutex_init(&mhi_cntrl->event_lock);
 
 	/* Set MHI version and AMSS EE before enumeration */

drivers/bus/mhi/ep/sm.c

@@ -63,24 +63,23 @@ int mhi_ep_set_m0_state(struct mhi_ep_cntrl *mhi_cntrl)
 	int ret;
 
 	/* If MHI is in M3, resume suspended channels */
-	spin_lock_bh(&mhi_cntrl->state_lock);
+	mutex_lock(&mhi_cntrl->state_lock);
+
 	old_state = mhi_cntrl->mhi_state;
 	if (old_state == MHI_STATE_M3)
 		mhi_ep_resume_channels(mhi_cntrl);
 
 	ret = mhi_ep_set_mhi_state(mhi_cntrl, MHI_STATE_M0);
-	spin_unlock_bh(&mhi_cntrl->state_lock);
-
 	if (ret) {
 		mhi_ep_handle_syserr(mhi_cntrl);
-		return ret;
+		goto err_unlock;
 	}
 
 	/* Signal host that the device moved to M0 */
 	ret = mhi_ep_send_state_change_event(mhi_cntrl, MHI_STATE_M0);
 	if (ret) {
 		dev_err(dev, "Failed sending M0 state change event\n");
-		return ret;
+		goto err_unlock;
 	}
 
 	if (old_state == MHI_STATE_READY) {
@@ -88,11 +87,14 @@ int mhi_ep_set_m0_state(struct mhi_ep_cntrl *mhi_cntrl)
 		ret = mhi_ep_send_ee_event(mhi_cntrl, MHI_EE_AMSS);
 		if (ret) {
 			dev_err(dev, "Failed sending AMSS EE event\n");
-			return ret;
+			goto err_unlock;
 		}
 	}
 
-	return 0;
+err_unlock:
+	mutex_unlock(&mhi_cntrl->state_lock);
+
+	return ret;
 }
 
 int mhi_ep_set_m3_state(struct mhi_ep_cntrl *mhi_cntrl)
@@ -100,13 +102,12 @@ int mhi_ep_set_m3_state(struct mhi_ep_cntrl *mhi_cntrl)
 	struct device *dev = &mhi_cntrl->mhi_dev->dev;
 	int ret;
 
-	spin_lock_bh(&mhi_cntrl->state_lock);
-	ret = mhi_ep_set_mhi_state(mhi_cntrl, MHI_STATE_M3);
-	spin_unlock_bh(&mhi_cntrl->state_lock);
+	mutex_lock(&mhi_cntrl->state_lock);
 
+	ret = mhi_ep_set_mhi_state(mhi_cntrl, MHI_STATE_M3);
 	if (ret) {
 		mhi_ep_handle_syserr(mhi_cntrl);
-		return ret;
+		goto err_unlock;
 	}
 
 	mhi_ep_suspend_channels(mhi_cntrl);
@@ -115,10 +116,13 @@ int mhi_ep_set_m3_state(struct mhi_ep_cntrl *mhi_cntrl)
 	ret = mhi_ep_send_state_change_event(mhi_cntrl, MHI_STATE_M3);
 	if (ret) {
 		dev_err(dev, "Failed sending M3 state change event\n");
-		return ret;
+		goto err_unlock;
 	}
 
-	return 0;
+err_unlock:
+	mutex_unlock(&mhi_cntrl->state_lock);
+
+	return ret;
 }
 
 int mhi_ep_set_ready_state(struct mhi_ep_cntrl *mhi_cntrl)
@@ -127,22 +131,24 @@ int mhi_ep_set_ready_state(struct mhi_ep_cntrl *mhi_cntrl)
 	enum mhi_state mhi_state;
 	int ret, is_ready;
 
-	spin_lock_bh(&mhi_cntrl->state_lock);
+	mutex_lock(&mhi_cntrl->state_lock);
+
 	/* Ensure that the MHISTATUS is set to RESET by host */
 	mhi_state = mhi_ep_mmio_masked_read(mhi_cntrl, EP_MHISTATUS, MHISTATUS_MHISTATE_MASK);
 	is_ready = mhi_ep_mmio_masked_read(mhi_cntrl, EP_MHISTATUS, MHISTATUS_READY_MASK);
 
 	if (mhi_state != MHI_STATE_RESET || is_ready) {
 		dev_err(dev, "READY state transition failed. MHI host not in RESET state\n");
-		spin_unlock_bh(&mhi_cntrl->state_lock);
-		return -EIO;
+		ret = -EIO;
+		goto err_unlock;
 	}
 
 	ret = mhi_ep_set_mhi_state(mhi_cntrl, MHI_STATE_READY);
-	spin_unlock_bh(&mhi_cntrl->state_lock);
-
 	if (ret)
 		mhi_ep_handle_syserr(mhi_cntrl);
 
+err_unlock:
+	mutex_unlock(&mhi_cntrl->state_lock);
+
 	return ret;
 }

include/linux/mhi_ep.h

@@ -70,8 +70,8 @@ struct mhi_ep_db_info {
  * @cmd_ctx_cache_phys: Physical address of the host command context cache
  * @chdb: Array of channel doorbell interrupt info
  * @event_lock: Lock for protecting event rings
- * @list_lock: Lock for protecting state transition and channel doorbell lists
  * @state_lock: Lock for protecting state transitions
+ * @list_lock: Lock for protecting state transition and channel doorbell lists
  * @st_transition_list: List of state transitions
  * @ch_db_list: List of queued channel doorbells
  * @wq: Dedicated workqueue for handling rings and state changes
@@ -117,8 +117,8 @@ struct mhi_ep_cntrl {
 
 	struct mhi_ep_db_info chdb[4];
 	struct mutex event_lock;
+	struct mutex state_lock;
 	spinlock_t list_lock;
-	spinlock_t state_lock;
 
 	struct list_head st_transition_list;
 	struct list_head ch_db_list;