[PATCH] vt: refactor console SAK processing

This does several things.
- It moves looking up of the current foreground console into process
  context where we can safely take the semaphore that protects this
  operation.
- It uses the new flavor of work queue processing.
- This generates a factor of do_SAK, __do_SAK that runs immediately.
- This calls __do_SAK with the console semaphore held ensuring nothing
  else happens to the console while we process the SAK operation.
- With the console SAK processing moved into process context this
  patch removes the xchg operations that I used to attempt to attomically
  update struct pid, because of the strange locking used in the SAK processing.
  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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 7fd3cd5..3757610 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -88,9 +88,9 @@ 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);
+	struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
+	PREPARE_WORK(SAK_work, vc_SAK);
+	schedule_work(SAK_work);
 }
 static struct sysrq_key_op sysrq_SAK_op = {
 	.handler	= sysrq_handle_SAK,