Commit e884a8a0 authored by Takashi Sakamoto's avatar Takashi Sakamoto
Browse files

firewire: core: call FCP address handlers outside RCU read-side critical section 

The former commit added reference counting to ensure safe invocations of
address handlers. Unlike the exclusive-region address handlers, all FCP
address handlers should be called on receiving an FCP request.

This commit uses the part of kernel stack to collect address handlers up
to 4 within the section, then invoke them outside of the section.
Reference counting ensures that each handler remains valid and safe to
call.

Lifting the limitation of supporting only 4 handlers is left for next
work.

Link: https://lore.kernel.org/r/20250803122015.236493-4-o-takashi@sakamocchi.jp


Signed-off-by: default avatarTakashi Sakamoto <o-takashi@sakamocchi.jp>
parent e8cf6875

drivers/firewire/core-transaction.c

+19 −6
Original line number Diff line number Diff line
@@ -950,13 +950,17 @@ static void handle_exclusive_region_request(struct fw_card *card, 
	put_address_handler(handler);

}



// To use kmalloc allocator efficiently, this should be power of two.

#define BUFFER_ON_KERNEL_STACK_SIZE	4



static void handle_fcp_region_request(struct fw_card *card,

				      struct fw_packet *p,

				      struct fw_request *request,

				      unsigned long long offset)

{

	struct fw_address_handler *handler;

	int tcode, destination, source;

	struct fw_address_handler *buffer_on_kernel_stack[BUFFER_ON_KERNEL_STACK_SIZE];

	struct fw_address_handler *handler, **handlers;

	int tcode, destination, source, i, count;



	if ((offset != (CSR_REGISTER_BASE | CSR_FCP_COMMAND) &&

	     offset != (CSR_REGISTER_BASE | CSR_FCP_RESPONSE)) ||
@@ -977,17 +981,26 @@ static void handle_fcp_region_request(struct fw_card *card, 
		return;

	}



	count = 0;

	handlers = buffer_on_kernel_stack;

	scoped_guard(rcu) {

		list_for_each_entry_rcu(handler, &address_handler_list, link) {

			if (is_enclosing_handler(handler, offset, request->length)) {

				get_address_handler(handler);

				handlers[count] = handler;

				if (++count >= ARRAY_SIZE(buffer_on_kernel_stack))

					break;

			}

		}

	}



	for (i = 0; i < count; ++i) {

		handler = handlers[i];

		handler->address_callback(card, request, tcode, destination, source,

					  p->generation, offset, request->data,

					  request->length, handler->callback_data);

		put_address_handler(handler);

	}

		}

	}



	fw_send_response(card, request, RCODE_COMPLETE);

}