[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>

diff --git a/drivers/char/keyboard.c b/drivers/char/keyboard.c
index 7a6c1c0b7a95861f9e4a70c4d6dca302491e5987..c654a3e0c697b36f008b934a8ed276bb6c110373 100644 (file)
--- a/drivers/char/keyboard.c
+++ b/drivers/char/keyboard.c
@@ -595,15 +595,9 @@ static void fn_spawn_con(struct vc_data *vc)
 
 static void fn_SAK(struct vc_data *vc)
 {
-       struct tty_struct *tty = vc->vc_tty;
-
-       /*
-        * SAK should also work in all raw modes and reset
-        * them properly.
-        */
-       if (tty)
-               do_SAK(tty);
-       reset_vc(vc);
+       struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
+       PREPARE_WORK(SAK_work, vc_SAK);
+       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 7fd3cd5ddf2190269e206383ece44c481a889f78..3757610b7835d4952e992563821293e6cc781fcd 100644 (file)
--- 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,

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 47a6eacb10bc4c0c49dc54357be1f7adf9e36fd7..c57b1f434652ac4be95d8182067c71ba272c2895 100644 (file)
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -3324,10 +3324,8 @@ int tty_ioctl(struct inode * inode, struct file * file,
  * Nasty bug: do_SAK is being called in interrupt context.  This can
  * deadlock.  We punt it up to process context.  AKPM - 16Mar2001
  */
-static void __do_SAK(struct work_struct *work)
+void __do_SAK(struct tty_struct *tty)
 {
-       struct tty_struct *tty =
-               container_of(work, struct tty_struct, SAK_work);
 #ifdef TTY_SOFT_SAK
        tty_hangup(tty);
 #else
@@ -3394,6 +3392,13 @@ static void __do_SAK(struct work_struct *work)
 #endif
 }
 
+static void do_SAK_work(struct work_struct *work)
+{
+       struct tty_struct *tty =
+               container_of(work, struct tty_struct, SAK_work);
+       __do_SAK(tty);
+}
+
 /*
  * The tq handling here is a little racy - tty->SAK_work may already be queued.
  * Fortunately we don't need to worry, because if ->SAK_work is already queued,
@@ -3404,7 +3409,7 @@ void do_SAK(struct tty_struct *tty)
 {
        if (!tty)
                return;
-       PREPARE_WORK(&tty->SAK_work, __do_SAK);
+       PREPARE_WORK(&tty->SAK_work, do_SAK_work);
        schedule_work(&tty->SAK_work);
 }
 

diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index dc8368ebb1ac932c2a8b18427b7197bdab371d82..3a5d301e783b062617f3e7043b42670e33ca2be2 100644 (file)
--- 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 +1064,35 @@ 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 vc_SAK(struct work_struct *work)
+{
+       struct vc *vc_con =
+               container_of(work, struct vc, SAK_work);
+       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/console_struct.h b/include/linux/console_struct.h
index ed6c0fee1ac76fa5af1e0ed27c26a6b6fbc86395..a86162b26c0dde5a349a81129e67b74f1506d821 100644 (file)
--- 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 65cbcf22c31e1e8ab7aef22b3b8da180825cf7cc..0161a8c6dbf6f638d7e95af33fe9a1656b0b4c9d 100644 (file)
--- 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);