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authorPeter Hurley <peter@hurleysoftware.com>2016-01-11 09:41:01 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2016-01-28 02:01:44 +0300
commite55afd11a48354c810caf6b6ad4c103016a88230 (patch)
treeeb073c28c1e21785fcbe92740ce1290da7fcb85c /drivers/tty/tty_ldisc.c
parent5b6e6832f41c9422753804671ee06af37ac8caf6 (diff)
downloadlinux-e55afd11a48354c810caf6b6ad4c103016a88230.tar.xz
tty: Prepare for destroying line discipline on hangup
tty file_operations (read/write/ioctl) wait for the ldisc reference indefinitely (until ldisc lifetime events, such as hangup or TIOCSETD, finish). Since hangup now destroys the ldisc and does not instance another copy, file_operations must now be prepared to receive a NULL ldisc reference from tty_ldisc_ref_wait(): CPU 0 CPU 1 ----- ----- (*f_op->read)() => tty_read() __tty_hangup() ... f_op = &hung_up_tty_fops; ... tty_ldisc_hangup() tty_ldisc_lock() tty_ldisc_kill() tty->ldisc = NULL tty_ldisc_unlock() ld = tty_ldisc_ref_wait() /* ld == NULL */ Instead, the action taken now is to return the same value as if the tty had been hungup a moment earlier: CPU 0 CPU 1 ----- ----- __tty_hangup() ... f_op = &hung_up_tty_fops; (*f_op->read)() => hung_up_tty_read() return 0; ... tty_ldisc_hangup() tty_ldisc_lock() tty_ldisc_kill() tty->ldisc = NULL tty_ldisc_unlock() 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.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 14d2165ba270..d6805e1aee59 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -262,8 +262,8 @@ const struct file_operations tty_ldiscs_proc_fops = {
* against a discipline change, such as an existing ldisc reference
* (which we check for)
*
- * Note: only callable from a file_operations routine (which
- * guarantees tty->ldisc != NULL when the lock is acquired).
+ * Note: a file_operations routine (read/poll/write) should use this
+ * function to wait for any ldisc lifetime events to finish.
*/
struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)