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>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index db04ec5121cb..191501afd7fb 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -265,8 +265,16 @@ typedef void (*fw_transaction_callback_t)(struct fw_card *card, int rcode,
 					  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,