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authorPeter Hurley <peter@hurleysoftware.com>2016-01-10 22:41:06 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-01-27 15:01:44 -0800
commit892d1fa7eaaed9d3c04954cb140c34ebc3393932 (patch)
treec85eb2b4043f4dcac9a57f610dd1aee7c9be1070 /drivers/tty/tty_ldisc.c
parent7896f30d6fc602f02198999acca4840620288990 (diff)
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tty: Destroy ldisc instance on hangup
Currently, when the tty is hungup, the ldisc is re-instanced; ie., the current instance is destroyed and a new instance is created. The purpose of this design was to guarantee a valid, open ldisc for the lifetime of the tty. However, now that tty buffers are owned by and have lifetime equivalent to the tty_port (since v3.10), any data received immediately after the ldisc is re-instanced may cause continued driver i/o operations concurrently with the driver's hangup() operation. For drivers that shutdown h/w on hangup, this is unexpected and usually bad. For example, the serial core may free the xmit buffer page concurrently with an in-progress write() operation (triggered by echo). With the existing stable and robust ldisc reference handling, the cleaned-up tty_reopen(), the straggling unsafe ldisc use cleaned up, and the preparation to properly handle a NULL tty->ldisc, the ldisc instance can be destroyed and only re-instanced when the tty is re-opened. If the tty was opened as /dev/console or /dev/tty0, the original behavior of re-instancing the ldisc is retained (the 'reinit' parameter to tty_ldisc_hangup() is true). This is required since those file descriptors are never hungup. This patch has neglible impact on userspace; the tty file_operations ptr is changed to point to the hungup file operations _before_ the ldisc instance is destroyed, so only racing file operations might now retrieve a NULL ldisc reference (which is simply handled as if the hungup file operation had been called instead -- see "tty: Prepare for destroying line discipline on hangup"). This resolves a long-standing FIXME and several crash reports. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/tty_ldisc.c')
-rw-r--r--drivers/tty/tty_ldisc.c40
1 files changed, 17 insertions, 23 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index e18c8e864110..c6f970d63060 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -257,6 +257,9 @@ const struct file_operations tty_ldiscs_proc_fops = {
* reference to it. If the line discipline is in flux then
* wait patiently until it changes.
*
+ * Returns: NULL if the tty has been hungup and not re-opened with
+ * a new file descriptor, otherwise valid ldisc reference
+ *
* Note: Must not be called from an IRQ/timer context. The caller
* must also be careful not to hold other locks that will deadlock
* against a discipline change, such as an existing ldisc reference
@@ -642,14 +645,15 @@ static void tty_reset_termios(struct tty_struct *tty)
* @disc: line discipline to reinitialize
*
* Completely reinitialize the line discipline state, by closing the
- * current instance and opening a new instance. If an error occurs opening
- * the new non-N_TTY instance, the instance is dropped and tty->ldisc reset
- * to NULL. The caller can then retry with N_TTY instead.
+ * current instance, if there is one, and opening a new instance. If
+ * an error occurs opening the new non-N_TTY instance, the instance
+ * is dropped and tty->ldisc reset to NULL. The caller can then retry
+ * with N_TTY instead.
*
* Returns 0 if successful, otherwise error code < 0
*/
-static int tty_ldisc_reinit(struct tty_struct *tty, int disc)
+int tty_ldisc_reinit(struct tty_struct *tty, int disc)
{
struct tty_ldisc *ld;
int retval;
@@ -693,11 +697,9 @@ static int tty_ldisc_reinit(struct tty_struct *tty, int disc)
* tty itself so we must be careful about locking rules.
*/
-void tty_ldisc_hangup(struct tty_struct *tty)
+void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
{
struct tty_ldisc *ld;
- int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS;
- int err = 0;
tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc);
@@ -725,25 +727,17 @@ void tty_ldisc_hangup(struct tty_struct *tty)
*/
tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT);
- if (tty->ldisc) {
+ if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS)
+ tty_reset_termios(tty);
- /* At this point we have a halted ldisc; we want to close it and
- reopen a new ldisc. We could defer the reopen to the next
- open but it means auditing a lot of other paths so this is
- a FIXME */
- if (reset == 0)
- err = tty_ldisc_reinit(tty, tty->termios.c_line);
-
- /* If the re-open fails or we reset then go to N_TTY. The
- N_TTY open cannot fail */
- if (reset || err < 0)
- tty_ldisc_reinit(tty, N_TTY);
+ if (tty->ldisc) {
+ if (reinit) {
+ if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0)
+ tty_ldisc_reinit(tty, N_TTY);
+ } else
+ tty_ldisc_kill(tty);
}
tty_ldisc_unlock(tty);
- if (reset)
- tty_reset_termios(tty);
-
- tty_ldisc_debug(tty, "%p: re-opened\n", tty->ldisc);
}
/**