[PATCH] vt: Make SAK run in process context.

[ebiederm@xmission.com (Eric W. Biederman)]

This defers SAK so we can use the normal console semaphore to order
operations.

This removes the xchg operations that I used to attempt to attmically
update struct pid, because of the strange locking used for SAK.  With
SAK using the normal console semaphore nothing special is needed.

Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 drivers/char/keyboard.c |   11 +++--------
 drivers/char/sysrq.c    |    7 ++++---
 drivers/char/vt_ioctl.c |   27 +++++++++++++++++++++++++--
 include/linux/vt_kern.h |    1 +
 4 files changed, 33 insertions(+), 13 deletions(-)

diff --git a/drivers/char/keyboard.c b/drivers/char/keyboard.c
index 7a6c1c0..bd6912d 100644
--- a/drivers/char/keyboard.c
+++ b/drivers/char/keyboard.c
@@ -595,15 +595,10 @@ static void fn_spawn_con(struct vc_data *vc)
 
 static void fn_SAK(struct vc_data *vc)
 {
-	struct tty_struct *tty = vc->vc_tty;
+	static DECLARE_WORK(SAK_work, deferred_SAK, NULL);
+	SAK_work.data = &vc_cons[fg_console];
 
-	/*
-	 * SAK should also work in all raw modes and reset
-	 * them properly.
-	 */
-	if (tty)
-		do_SAK(tty);
-	reset_vc(vc);
+	schedule_work(&SAK_work);
 }
 
 static void fn_null(struct vc_data *vc)
diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 05810c8..b4f67a0 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -61,9 +61,10 @@ static struct sysrq_key_op sysrq_loglevel_op = {
 #ifdef CONFIG_VT
 static void sysrq_handle_SAK(int key, struct tty_struct *tty)
 {
-	if (tty)
-		do_SAK(tty);
-	reset_vc(vc_cons[fg_console].d);
+	static DECLARE_WORK(SAK_work, deferred_SAK, NULL);
+	SAK_work.data = &vc_cons[fg_console];
+
+	schedule_work(&SAK_work);
 }
 static struct sysrq_key_op sysrq_SAK_op = {
 	.handler	= sysrq_handle_SAK,
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 311493e..5ecc71e 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -672,7 +672,8 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
 		vc->vt_mode = tmp;
 		/* the frsig is ignored, so we set it to 0 */
 		vc->vt_mode.frsig = 0;
-		put_pid(xchg(&vc->vt_pid, get_pid(task_pid(current))));
+		put_pid(vc->vt_pid);
+		vc->vt_pid = get_pid(task_pid(current));
 		/* no switch is required -- saw@shade.msu.ru */
 		vc->vt_newvt = -1;
 		release_console_sem();
@@ -1063,12 +1064,34 @@ void reset_vc(struct vc_data *vc)
 	vc->vt_mode.relsig = 0;
 	vc->vt_mode.acqsig = 0;
 	vc->vt_mode.frsig = 0;
-	put_pid(xchg(&vc->vt_pid, NULL));
+	put_pid(vc->vt_pid);
+	vc->vt_pid = NULL;
 	vc->vt_newvt = -1;
 	if (!in_interrupt())    /* Via keyboard.c:SAK() - akpm */
 		reset_palette(vc);
 }
 
+void deferred_SAK(void *data)
+{
+	struct vc *vc_con = data;
+	struct vc_data *vc;
+	struct tty_struct *tty;
+	
+	acquire_console_sem();
+	vc = vc_con->d;
+	if (vc) {
+		tty = vc->vc_tty;
+		/*
+		 * SAK should also work in all raw modes and reset
+		 * them properly.
+		 */
+		if (tty)
+			do_SAK(tty);
+		reset_vc(vc);
+	}
+	release_console_sem();
+}
+
 /*
  * Performs the back end of a vt switch
  */
diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
index 37a1a41..a727896 100644
--- a/include/linux/vt_kern.h
+++ b/include/linux/vt_kern.h
@@ -74,6 +74,7 @@ int con_copy_unimap(struct vc_data *dst_vc, struct vc_data *src_vc);
 int vt_waitactive(int vt);
 void change_console(struct vc_data *new_vc);
 void reset_vc(struct vc_data *vc);
+void deferred_SAK(void *data);
 
 /*
  * vc_screen.c shares this temporary buffer with the console write code so that
-- 
1.4.4.1.g278f