tty: Fix ref counting for port krefs

The tty core supports two models for handling tty_port lifetimes;
the tty_port can use the kref supplied by tty_port (which will
automatically destruct the tty_port when the ref count drops to
zero) or it can destruct the tty_port manually.

For tty drivers that choose to use the port kref to manage the
tty_port lifetime, it is not possible to safely acquire a port
reference conditionally. If the last reference is released after
evaluating the condition but before acquiring the reference, a
bogus reference will be held while the tty_port destruction
commences.

Rather, only acquire a port reference if the ref count is non-zero
and allow the caller to distinguish if a reference has successfully
been acquired.

Cc: Jiri Slaby <[email protected]>
Signed-off-by: Peter Hurley <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Tested-By: Alexander Holler <[email protected]>
Signed-off-by: Marcel Holtmann <[email protected]>

0 files changed, 0 insertions, 0 deletions