[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>

2 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
index ed6c0fee1ac7..a86162b26c0d 100644
--- a/include/linux/console_struct.h
+++ b/include/linux/console_struct.h
@@ -11,6 +11,7 @@
 
 #include <linux/wait.h>
 #include <linux/vt.h>
+#include <linux/workqueue.h>
 
 struct vt_struct;
 
@@ -103,6 +104,7 @@ struct vc_data {
 
 struct vc {
         struct vc_data *d;
+        struct work_struct SAK_work;
 
         /* might add  scrmem, vt_struct, kbd  at some time,
            to have everything in one place - the disadvantage
@@ -110,6 +112,7 @@ struct vc {
 };
 
 extern struct vc vc_cons [MAX_NR_CONSOLES];
+extern void vc_SAK(struct work_struct *work);
 
 #define CUR_DEF         0
 #define CUR_NONE        1
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 65cbcf22c31e..0161a8c6dbf6 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -291,6 +291,7 @@ extern void tty_vhangup(struct tty_struct * tty);
 extern void tty_unhangup(struct file *filp);
 extern int tty_hung_up_p(struct file * filp);
 extern void do_SAK(struct tty_struct *tty);
+extern void __do_SAK(struct tty_struct *tty);
 extern void disassociate_ctty(int priv);
 extern void tty_flip_buffer_push(struct tty_struct *tty);
 extern speed_t tty_get_baud_rate(struct tty_struct *tty);