firewire: core: use mutex instead of spinlock for client isochronous context

There is a restriction that the userspace client associated to a file
descriptor can hold one isochronous context. The client-level spinning
lock is used to guarantee it, however the lock is also used for
multi-purposes. Additionally, there is no need to use this type of lock,
and the mutex is available, instead.

Link: https://lore.kernel.org/r/20260110013911.19160-3-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
index 49dc1612c6911e25c46a5bd1f6c85ead7c4c9011..2b8a878c8aae64781dd244fb0eaed8446980dcbc 100644 (file)
--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -63,6 +63,7 @@ struct client {
        u64 bus_reset_closure;
 
        struct fw_iso_context *iso_context;
+       struct mutex iso_context_mutex;
        u64 iso_closure;
        struct fw_iso_buffer buffer;
        unsigned long vm_start;
@@ -306,6 +307,7 @@ static int fw_device_op_open(struct inode *inode, struct file *file)
        INIT_LIST_HEAD(&client->phy_receiver_link);
        INIT_LIST_HEAD(&client->link);
        kref_init(&client->kref);
+       mutex_init(&client->iso_context_mutex);
 
        file->private_data = client;
 
@@ -1088,26 +1090,27 @@ static int ioctl_create_iso_context(struct client *client, union ioctl_arg *arg)
                context->drop_overflow_headers = true;
 
        // We only support one context at this time.
-       guard(spinlock_irq)(&client->lock);
-
-       if (client->iso_context != NULL) {
-               fw_iso_context_destroy(context);
-
-               return -EBUSY;
-       }
-       if (!client->buffer_is_mapped) {
-               ret = fw_iso_buffer_map_dma(&client->buffer,
-                                           client->device->card,
-                                           iso_dma_direction(context));
-               if (ret < 0) {
+       scoped_guard(mutex, &client->iso_context_mutex) {
+               if (client->iso_context != NULL) {
                        fw_iso_context_destroy(context);
 
-                       return ret;
+                       return -EBUSY;
                }
-               client->buffer_is_mapped = true;
+               // The DMA mapping operation is available if the buffer is already allocated by
+               // mmap(2) system call. If not, it is delegated to the system call.
+               if (!client->buffer_is_mapped) {
+                       ret = fw_iso_buffer_map_dma(&client->buffer, client->device->card,
+                                                   iso_dma_direction(context));
+                       if (ret < 0) {
+                               fw_iso_context_destroy(context);
+
+                               return ret;
+                       }
+                       client->buffer_is_mapped = true;
+               }
+               client->iso_closure = a->closure;
+               client->iso_context = context;
        }
-       client->iso_closure = a->closure;
-       client->iso_context = context;
 
        a->handle = 0;
 
@@ -1826,7 +1829,9 @@ static int fw_device_op_mmap(struct file *file, struct vm_area_struct *vma)
        if (ret < 0)
                return ret;
 
-       scoped_guard(spinlock_irq, &client->lock) {
+       scoped_guard(mutex, &client->iso_context_mutex) {
+               // The direction of DMA can be determined if the isochronous context is already
+               // allocated. If not, the DMA mapping operation is postponed after the allocation.
                if (client->iso_context) {
                        ret = fw_iso_buffer_map_dma(&client->buffer, client->device->card,
                                                    iso_dma_direction(client->iso_context));
@@ -1879,6 +1884,7 @@ static int fw_device_op_release(struct inode *inode, struct file *file)
 
        if (client->iso_context)
                fw_iso_context_destroy(client->iso_context);
+       mutex_destroy(&client->iso_context_mutex);
 
        if (client->buffer.pages)
                fw_iso_buffer_destroy(&client->buffer, client->device->card);