On Mon, Jun 16, 2014 at 09:17:06AM -0400, Peter Hurley wrote:
> Since at least before 2.6.30, it has not been possible to observe
> a hung up file pointer in a tty driver's open() method unless/until
> the driver open() releases the tty_lock() (eg., before blocking).
>
> This is because tty_open() adds the file pointer while holding
> the tty_lock() _and_ doesn't release the lock until after calling
> the tty driver's open() method. [ Before tty_lock(), this was
> lock_kernel(). ]
>
> Since __tty_hangup() first waits on the tty_lock() before
> enumerating and hanging up the open file pointers, either
> __tty_hangup() will wait for the tty_lock() or tty_open() will
> not yet have added the file pointer. For example,
>
> CPU 0 | CPU 1
> |
> tty_open | __tty_hangup
> .. | ..
> tty_lock | ..
> tty_reopen | tty_lock / blocks
> .. |
> tty_add_file(tty, filp) |
> .. |
> tty->ops->open(tty, filp) |
> tty_port_open |
> tty_port_block_til_ready |
> .. |
> while (1) |
> .. |
> tty_unlock | / unblocks
> schedule | for each filp on tty->tty_files
> | f_ops = tty_hung_up_fops;
> | ..
> | tty_unlock
> tty_lock |
> .. |
> tty_unlock |
>
> Note that since tty_port_block_til_ready() and similar drop
> the tty_lock while blocking, when woken, the file pointer
> must then be tested for having been hung up.
>
> Also, fix bit-rotted drivers that used extra_count to track the
> port->count bump.
>
> CC: Mikael Starvik <starvik@xxxxxxxx>
For the CRIS part:
Acked-by: Jesper Nilsson <jesper.nilsson@xxxxxxxx>
> CC: Samuel Ortiz <samuel@xxxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
/^JN - Jesper Nilsson
--
Jesper Nilsson -- jesper.nilsson@xxxxxxxx
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