firmware: arm_ffa: Replace mutex with rwlock to avoid sleep in atomic context

JIRA: https://issues.redhat.com/browse/RHEL-102692

commit 9ca7a42
Author: Sudeep Holla <sudeep.holla@arm.com>
Date: Wed, 28 May 2025 09:49:43 +0100

    The current use of a mutex to protect the notifier hashtable accesses
    can lead to issues in the atomic context. It results in the below
    kernel warnings:

      |  BUG: sleeping function called from invalid context at kernel/locking/mutex.c:258
      |  in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 9, name: kworker/0:0
      |  preempt_count: 1, expected: 0
      |  RCU nest depth: 0, expected: 0
      |  CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted 6.14.0 #4
      |  Workqueue: ffa_pcpu_irq_notification notif_pcpu_irq_work_fn
      |  Call trace:
      |   show_stack+0x18/0x24 (C)
      |   dump_stack_lvl+0x78/0x90
      |   dump_stack+0x18/0x24
      |   __might_resched+0x114/0x170
      |   __might_sleep+0x48/0x98
      |   mutex_lock+0x24/0x80
      |   handle_notif_callbacks+0x54/0xe0
      |   notif_get_and_handle+0x40/0x88
      |   generic_exec_single+0x80/0xc0
      |   smp_call_function_single+0xfc/0x1a0
      |   notif_pcpu_irq_work_fn+0x2c/0x38
      |   process_one_work+0x14c/0x2b4
      |   worker_thread+0x2e4/0x3e0
      |   kthread+0x13c/0x210
      |   ret_from_fork+0x10/0x20

    To address this, replace the mutex with an rwlock to protect the notifier
    hashtable accesses. This ensures that read-side locking does not sleep and
    multiple readers can acquire the lock concurrently, avoiding unnecessary
    contention and potential deadlocks. Writer access remains exclusive,
    preserving correctness.

    This change resolves warnings from lockdep about potential sleep in
    atomic context.

    Cc: Jens Wiklander <jens.wiklander@linaro.org>
    Reported-by: Jérôme Forissier <jerome.forissier@linaro.org>
    Closes: OP-TEE/optee_os#7394
    Fixes: e057344 ("firmware: arm_ffa: Add interfaces to request notification callbacks")
    Message-Id: <20250528-ffa_notif_fix-v1-3-5ed7bc7f8437@arm.com>
    Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
    Tested-by: Jens Wiklander <jens.wiklander@linaro.org>
    Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Signed-off-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>
Message-ID: <d2632a513f05ec79f4fffa92d618792eb3cea12f.1752653152.git.mjuszkiewicz@redhat.com>
Message-ID: <b4e3e2e1248ca9909bdea280d9009bdb659d0c81.1752659027.git.mjuszkiewicz@redhat.com>

Author: hrw

drivers/firmware/arm_ffa/driver.c

@@ -110,7 +110,7 @@ struct ffa_drv_info {
 	struct work_struct sched_recv_irq_work;
 	struct xarray partition_info;
 	DECLARE_HASHTABLE(notifier_hash, ilog2(FFA_MAX_NOTIFICATIONS));
-	struct mutex notify_lock; /* lock to protect notifier hashtable  */
+	rwlock_t notify_lock; /* lock to protect notifier hashtable  */
 };
 
 static struct ffa_drv_info *drv_info;
@@ -1289,19 +1289,19 @@ static int __ffa_notify_relinquish(struct ffa_device *dev, int notify_id,
 	if (notify_id >= FFA_MAX_NOTIFICATIONS)
 		return -EINVAL;
 
-	mutex_lock(&drv_info->notify_lock);
+	write_lock(&drv_info->notify_lock);
 
 	rc = update_notifier_cb(dev, notify_id, NULL, is_framework);
 	if (rc) {
 		pr_err("Could not unregister notification callback\n");
-		mutex_unlock(&drv_info->notify_lock);
+		write_unlock(&drv_info->notify_lock);
 		return rc;
 	}
 
 	if (!is_framework)
 		rc = ffa_notification_unbind(dev->vm_id, BIT(notify_id));
 
-	mutex_unlock(&drv_info->notify_lock);
+	write_unlock(&drv_info->notify_lock);
 
 	return rc;
 }
@@ -1341,7 +1341,7 @@ static int __ffa_notify_request(struct ffa_device *dev, bool is_per_vcpu,
 	else
 		cb_info->cb = cb;
 
-	mutex_lock(&drv_info->notify_lock);
+	write_lock(&drv_info->notify_lock);
 
 	if (!is_framework) {
 		if (is_per_vcpu)
@@ -1361,7 +1361,7 @@ static int __ffa_notify_request(struct ffa_device *dev, bool is_per_vcpu,
 	}
 
 out_unlock_free:
-	mutex_unlock(&drv_info->notify_lock);
+	write_unlock(&drv_info->notify_lock);
 	if (rc)
 		kfree(cb_info);
 
@@ -1407,9 +1407,9 @@ static void handle_notif_callbacks(u64 bitmap, enum notify_type type)
 		if (!(bitmap & 1))
 			continue;
 
-		mutex_lock(&drv_info->notify_lock);
+		read_lock(&drv_info->notify_lock);
 		cb_info = notifier_hnode_get_by_type(notify_id, type);
-		mutex_unlock(&drv_info->notify_lock);
+		read_unlock(&drv_info->notify_lock);
 
 		if (cb_info && cb_info->cb)
 			cb_info->cb(notify_id, cb_info->cb_data);
@@ -1447,9 +1447,9 @@ static void handle_fwk_notif_callbacks(u32 bitmap)
 
 	ffa_rx_release();
 
-	mutex_lock(&drv_info->notify_lock);
+	read_lock(&drv_info->notify_lock);
 	cb_info = notifier_hnode_get_by_vmid_uuid(notify_id, target, &uuid);
-	mutex_unlock(&drv_info->notify_lock);
+	read_unlock(&drv_info->notify_lock);
 
 	if (cb_info && cb_info->fwk_cb)
 		cb_info->fwk_cb(notify_id, cb_info->cb_data, buf);
@@ -1974,7 +1974,7 @@ static void ffa_notifications_setup(void)
 		goto cleanup;
 
 	hash_init(drv_info->notifier_hash);
-	mutex_init(&drv_info->notify_lock);
+	rwlock_init(&drv_info->notify_lock);
 
 	drv_info->notif_enabled = true;
 	return;