firewire: addendum to address handler RCU conversion
Follow up on commit c285f6ff6787 "firewire: remove global lock around
address handlers, convert to RCU":
- address_handler_lock no longer serializes the address handler, only
its function to serialize updates to the list of handlers remains.
Rename the lock to address_handler_list_lock.
- Callers of fw_core_remove_address_handler() must be able to sleep.
Comment on this in the API documentation.
- The counterpart fw_core_add_address_handler() is by nature something
which is used in process context. Replace spin_lock_bh() by
spin_lock() in fw_core_add_address_handler() and in
fw_core_remove_address_handler(), and document that process context
is now required for fw_core_add_address_handler().
- Extend the documentation of fw_address_callback_t.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index d39cfa4..28a94c7 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -519,7 +519,7 @@
return NULL;
}
-static DEFINE_SPINLOCK(address_handler_lock);
+static DEFINE_SPINLOCK(address_handler_list_lock);
static LIST_HEAD(address_handler_list);
const struct fw_address_region fw_high_memory_region =
@@ -556,6 +556,7 @@
* the specified callback is invoked. The parameters passed to the callback
* give the details of the particular request.
*
+ * To be called in process context.
* Return value: 0 on success, non-zero otherwise.
*
* The start offset of the handler's address region is determined by
@@ -576,7 +577,7 @@
handler->length == 0)
return -EINVAL;
- spin_lock_bh(&address_handler_lock);
+ spin_lock(&address_handler_list_lock);
handler->offset = region->start;
while (handler->offset + handler->length <= region->end) {
@@ -595,7 +596,7 @@
}
}
- spin_unlock_bh(&address_handler_lock);
+ spin_unlock(&address_handler_list_lock);
return ret;
}
@@ -604,14 +605,16 @@
/**
* fw_core_remove_address_handler() - unregister an address handler
*
+ * To be called in process context.
+ *
* When fw_core_remove_address_handler() returns, @handler->callback() is
* guaranteed to not run on any CPU anymore.
*/
void fw_core_remove_address_handler(struct fw_address_handler *handler)
{
- spin_lock_bh(&address_handler_lock);
+ spin_lock(&address_handler_list_lock);
list_del_rcu(&handler->link);
- spin_unlock_bh(&address_handler_lock);
+ spin_unlock(&address_handler_list_lock);
synchronize_rcu();
}
EXPORT_SYMBOL(fw_core_remove_address_handler);
diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index db04ec5..191501a 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -265,8 +265,16 @@
void *data, size_t length,
void *callback_data);
/*
- * Important note: Except for the FCP registers, the callback must guarantee
- * that either fw_send_response() or kfree() is called on the @request.
+ * This callback handles an inbound request subaction. It is called in
+ * RCU read-side context, therefore must not sleep.
+ *
+ * The callback should not initiate outbound request subactions directly.
+ * Otherwise there is a danger of recursion of inbound and outbound
+ * transactions from and to the local node.
+ *
+ * The callback is responsible that either fw_send_response() or kfree()
+ * is called on the @request, except for FCP registers for which the core
+ * takes care of that.
*/
typedef void (*fw_address_callback_t)(struct fw_card *card,
struct fw_request *request,