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When HCI_UART_PROTO_READY is in the set state, the Data Link protocol layer (proto) is bound to the HCI UART driver. This state allows the registered proto function pointers to be used by the HCI UART driver. When unbinding (closing) the Data Link protocol layer, the proto function pointers much be prevented from being used immediately before running the proto close function pointer. Otherwise, there is a risk that a proto non-close function pointer is used during or after the proto close function pointer is used. The consequences are likely to be a kernel crash because the proto close function pointer will free resources used in the Data Link protocol layer. Therefore, add a reader writer lock (rwlock) solution to prevent the close proto function pointer from running by using write_lock_irqsave() whilst the other proto function pointers are protected using read_lock(). This means HCI_UART_PROTO_READY can safely be cleared in the knowledge that no proto function pointers are running. When flag HCI_UART_PROTO_READY is put into the clear state, proto close function pointer can safely be run. Note flag HCI_UART_PROTO_SET being in the set state prevents the proto open function pointer from being run so there is no race condition between proto open and close function pointers. Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.