From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: linux-kernel@vger.kernel.org, greg@kroah.com
Subject: [RFC PATCH] vt: Fix deadlock on scroll-lock
Date: Tue, 01 May 2012 15:42:58 +0100 [thread overview]
Message-ID: <20120501144245.12381.49800.stgit@bob.linux.org.uk> (raw)
From: Alan Cox <alan@linux.intel.com>
Fixing the locking accidentally replaced a race in the scroll
lock handling with a deadlock. Turn it back into a race for
now.
The basic problem is that there are two paths into the tty
stop/start helpers. One via the tty layer ^S/^Q handling
where we need to take the kbd_event_lock and one via the
special keyboard handler for fn_hold where we already hold
it. Probably we need to split out into a separate LED lock
but for now just go back to the race as it's a bit close
to release.
Signed-off-by: Alan Cox <alan@linux.intel.com>
---
drivers/tty/vt/keyboard.c | 22 +++++++++++++++++-----
1 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 86dd1e3..6d54a6a 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -1085,15 +1085,21 @@ void vt_set_led_state(int console, int leds)
*
* Handle console start. This is a wrapper for the VT layer
* so that we can keep kbd knowledge internal
+ *
+ * FIXME: We eventually need to hold the kbd lock here to protect
+ * the LED updating. We can't do it yet because fn_hold calls stop_tty
+ * and start_tty under the kbd_event_lock, while normal tty paths
+ * don't hold the lock. We probably need to split out an LED lock
+ * but not during an -rc release!
*/
void vt_kbd_con_start(int console)
{
struct kbd_struct * kbd = kbd_table + console;
unsigned long flags;
- spin_lock_irqsave(&kbd_event_lock, flags);
+/* spin_lock_irqsave(&kbd_event_lock, flags); */
clr_vc_kbd_led(kbd, VC_SCROLLOCK);
set_leds();
- spin_unlock_irqrestore(&kbd_event_lock, flags);
+/* spin_unlock_irqrestore(&kbd_event_lock, flags); */
}
/**
@@ -1102,22 +1108,28 @@ void vt_kbd_con_start(int console)
*
* Handle console stop. This is a wrapper for the VT layer
* so that we can keep kbd knowledge internal
+ *
+ * FIXME: We eventually need to hold the kbd lock here to protect
+ * the LED updating. We can't do it yet because fn_hold calls stop_tty
+ * and start_tty under the kbd_event_lock, while normal tty paths
+ * don't hold the lock. We probably need to split out an LED lock
+ * but not during an -rc release!
*/
void vt_kbd_con_stop(int console)
{
struct kbd_struct * kbd = kbd_table + console;
unsigned long flags;
- spin_lock_irqsave(&kbd_event_lock, flags);
+/* spin_lock_irqsave(&kbd_event_lock, flags); */
set_vc_kbd_led(kbd, VC_SCROLLOCK);
set_leds();
- spin_unlock_irqrestore(&kbd_event_lock, flags);
+/* spin_unlock_irqrestore(&kbd_event_lock, flags); */
}
/*
* This is the tasklet that updates LED state on all keyboards
* attached to the box. The reason we use tasklet is that we
* need to handle the scenario when keyboard handler is not
- * registered yet but we already getting updates form VT to
+ * registered yet but we already getting updates from the VT to
* update led state.
*/
static void kbd_bh(unsigned long dummy)
reply other threads:[~2012-05-01 14:27 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20120501144245.12381.49800.stgit@bob.linux.org.uk \
--to=alan@lxorguk.ukuu.org.uk \
--cc=greg@kroah.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).