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serial: Fix locking for uart driver set_termios() method

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The low-level uart driver may modify termios settings to override
settings that are not compatible with the uart, such as CRTSCTS.
Thus, callers of the low-level uart driver's set_termios() method must
hold termios_rwsem write lock to prevent concurrent access to termios,
in case such override occurs.

The termios_rwsem lock requirement does not extend to console setup
(ie., uart_set_options), as console setup cannot race with tty
operations. Nor does this lock requirement extend to functions which
cannot be concurrent with tty ioctls (ie., uart_port_startup() and
uart_resume_port()).

Further, always claim the port mutex to protect hardware
re-reprogramming in the set_termios() uart driver method. Note this
is unnecessary for console initialization in uart_set_options()
which cannot be concurrent with other uart operations.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley
2014-10-16 16:54:20 -04:00
committed by Greg Kroah-Hartman
parent 2e75891083
commit 7c8ab967e3
2 changed files with 11 additions and 3 deletions
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6
Documentation/serial/driver
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@@ -59,7 +59,9 @@ The core driver uses the info->tmpbuf_sem lock to prevent multi-threaded
access to the info->tmpbuf bouncebuffer used for port writes.
The port_sem semaphore is used to protect against ports being added/
removed or reconfigured at inappropriate times.
removed or reconfigured at inappropriate times. Since v2.6.27, this
semaphore has been the 'mutex' member of the tty_port struct, and
commonly referred to as the port mutex (or port->mutex).
uart_ops
@@ -248,7 +250,7 @@ hardware.
Other flags may be used (eg, xon/xoff characters) if your
hardware supports hardware "soft" flow control.
Locking: none.
Locking: caller holds port->mutex
Interrupts: caller dependent.
This call must not sleep