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authorStefan Richter <stefanr@s5r6.in-berlin.de>2012-02-18 19:54:45 +0100
committerStefan Richter <stefanr@s5r6.in-berlin.de>2012-02-22 22:36:01 +0100
commit90963f1cdb3baffc68321e7c98073bf9e99d2ec7 (patch)
treef05b75602a799b48d38f751de20b879d87bd6c4a /drivers/firewire
parent280f64d4f108b7ac707d6208d50a59627b984dc5 (diff)
downloadlinux-90963f1cdb3baffc68321e7c98073bf9e99d2ec7.tar.bz2
firewire: core: fix race at address_handler unregistration
Fix the following unlikely but possible race: CPU 1 CPU 2 ------------------------------------------------------------------------ AR-request tasklet lookup handler unregister handler free handler->callback_data or handler call handler->callback The application which registered the handler has no way to stop nodes sending new requests to their address range, hence cannot prevent this race. Fix it simply by extending the address_handler_lock-protected region from only around the lookup to around both lookup and call. We only need to do so in the exclusive region handler; the FCP region handler already holds the lock around the handler->callback call. Alas this removes the current ability to execute the callback in parallel on different CPUs if it was called for different FireWire cards at the same time. (For a single card, the handler is already serialized.) If this loss of a rather obscure feature is not tolerable, a more complex fix would be required: Add a handler reference counter; wait in fw_core_remove_address_handler() for this conter to become zero. Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Diffstat (limited to 'drivers/firewire')
-rw-r--r--drivers/firewire/core-transaction.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index 89e310ba03ba..190bf61533a2 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -602,6 +602,9 @@ EXPORT_SYMBOL(fw_core_add_address_handler);
/**
* fw_core_remove_address_handler() - unregister an address handler
+ *
+ * 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)
{
@@ -838,16 +841,16 @@ static void handle_exclusive_region_request(struct fw_card *card,
spin_lock_irqsave(&address_handler_lock, flags);
handler = lookup_enclosing_address_handler(&address_handler_list,
offset, request->length);
- spin_unlock_irqrestore(&address_handler_lock, flags);
-
- if (handler == NULL)
- fw_send_response(card, request, RCODE_ADDRESS_ERROR);
- else
+ if (handler)
handler->address_callback(card, request,
tcode, destination, source,
p->generation, offset,
request->data, request->length,
handler->callback_data);
+ spin_unlock_irqrestore(&address_handler_lock, flags);
+
+ if (!handler)
+ fw_send_response(card, request, RCODE_ADDRESS_ERROR);
}
static void handle_fcp_region_request(struct fw_card *card,