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

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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: Takashi Sakamoto <o-takashi@sakamocchi.jp>
This commit is contained in:
Takashi Sakamoto
2025-08-03 21:20:14 +09:00
parent e8cf687500
commit e884a8a0c5
1 changed files with 19 additions and 6 deletions
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25
drivers/firewire/core-transaction.c
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@@ -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)) ||
@@ -977,18 +981,27 @@ 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);
handler->address_callback(card, request, tcode, destination, source,
p->generation, offset, request->data,
request->length, handler->callback_data);
put_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);
}