Messages in this thread | | | Date | Thu, 15 Mar 2012 10:08:12 +0000 | From | Alan Cox <> | Subject | Re: [PATCH] tty: hold lock across tty buffer finding and buffer filling |
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On Thu, 15 Mar 2012 02:06:43 +0000 "Tu, Xiaobing" <xiaobing.tu@intel.com> wrote:
> From: Xiaobing Tu <xiaobing.tu@intel.com> > > tty_buffer_request_room is well protected, but while after it returns, > it releases the port->lock. tty->buf.tail might be modified
This can only occur in a way that matters if you have multiple writers to the tty buffer.
It is a design requirement of the tty layer that your input is single threaded paths and this is true for existing drivers. There is a good reason it is true as well - ordering of bytes is defined for serial data, any parallel writer breaks that ordering even if you have locks in tty_insert_flip_*.
In practice that means that the tail pointer has a single incrementer and the reader is the ldisc processing queue.
So NAK pending a lot more explanation and an actual case where you can show it is required.
Under what situations with what in tree driver do you see a problem ?
Alan
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