118 lines
3.7 KiB
Diff
118 lines
3.7 KiB
Diff
From 4d458f558d5b904f14080b073b549d18c9503f93 Mon Sep 17 00:00:00 2001
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From: Jiri Slaby <jslaby@suse.cz>
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Date: Sun, 31 Oct 2010 23:17:51 +0100
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Subject: TTY: restore tty_ldisc_wait_idle
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It was removed in 65b770468e98 (tty-ldisc: turn ldisc user count into
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a proper refcount), but we need to wait for last user to quit the
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ldisc before we close it in tty_set_ldisc.
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Otherwise weird things start to happen. There might be processes
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waiting in tty_read->n_tty_read on tty->read_wait for input to appear
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and at that moment, a change of ldisc is fatal. n_tty_close is called,
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it frees read_buf and the waiting process is still in the middle of
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reading and goes nuts after it is woken.
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Previously we prevented close to happen when others are in ldisc ops
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by tty_ldisc_wait_idle in tty_set_ldisc. But the commit above removed
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that. So revoke the change and test whether there is 1 user (=we), and
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allow the close then.
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We can do that without ldisc/tty locks, because nobody else can open
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the device due to TTY_LDISC_CHANGING bit set, so we in fact wait for
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everybody to leave.
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I don't understand why tty_ldisc_lock would be needed either when the
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counter is an atomic variable, so this is a lockless
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tty_ldisc_wait_idle.
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On the other hand, if we fail to wait (timeout or signal), we have to
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reenable the halted ldiscs, so we take ldisc lock and reuse the setup
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path at the end of tty_set_ldisc.
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Signed-off-by: Jiri Slaby <jslaby@suse.cz>
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Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
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Tested-by: Sebastian Andrzej Siewior <bigeasy@breakpoint.cc>
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LKML-Reference: <20101031104136.GA511@Chamillionaire.breakpoint.cc>
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LKML-Reference: <1287669539-22644-1-git-send-email-jslaby@suse.cz>
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Cc: Alan Cox <alan@linux.intel.com>
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Cc: stable@kernel.org [32, 33, 36]
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Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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---
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drivers/char/tty_ldisc.c | 29 +++++++++++++++++++++++++++++
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1 files changed, 29 insertions(+), 0 deletions(-)
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diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
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index 412f977..5bbf33a 100644
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--- a/drivers/char/tty_ldisc.c
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+++ b/drivers/char/tty_ldisc.c
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@@ -47,6 +47,7 @@
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static DEFINE_SPINLOCK(tty_ldisc_lock);
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static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
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+static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
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/* Line disc dispatch table */
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static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
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@@ -83,6 +84,7 @@ static void put_ldisc(struct tty_ldisc *ld)
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return;
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}
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local_irq_restore(flags);
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+ wake_up(&tty_ldisc_idle);
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}
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/**
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@@ -531,6 +533,23 @@ static int tty_ldisc_halt(struct tty_struct *tty)
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}
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/**
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+ * tty_ldisc_wait_idle - wait for the ldisc to become idle
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+ * @tty: tty to wait for
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+ *
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+ * Wait for the line discipline to become idle. The discipline must
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+ * have been halted for this to guarantee it remains idle.
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+ */
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+static int tty_ldisc_wait_idle(struct tty_struct *tty)
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+{
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+ int ret;
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+ ret = wait_event_interruptible_timeout(tty_ldisc_idle,
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+ atomic_read(&tty->ldisc->users) == 1, 5 * HZ);
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+ if (ret < 0)
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+ return ret;
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+ return ret > 0 ? 0 : -EBUSY;
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+}
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+
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+/**
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* tty_set_ldisc - set line discipline
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* @tty: the terminal to set
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* @ldisc: the line discipline
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@@ -634,8 +653,17 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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flush_scheduled_work();
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+ retval = tty_ldisc_wait_idle(tty);
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+
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tty_lock();
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mutex_lock(&tty->ldisc_mutex);
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+
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+ /* handle wait idle failure locked */
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+ if (retval) {
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+ tty_ldisc_put(new_ldisc);
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+ goto enable;
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+ }
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+
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if (test_bit(TTY_HUPPED, &tty->flags)) {
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/* We were raced by the hangup method. It will have stomped
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the ldisc data and closed the ldisc down */
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@@ -669,6 +697,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc)
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tty_ldisc_put(o_ldisc);
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+enable:
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/*
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* Allow ldisc referencing to occur again
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*/
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--
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1.7.3.2
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