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Subject[PATCH] vt: Refactor console SAK processing.
Date

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>
---
drivers/char/keyboard.c | 12 +++---------
drivers/char/sysrq.c | 6 +++---
drivers/char/tty_io.c | 13 +++++++++----
drivers/char/vt_ioctl.c | 28 ++++++++++++++++++++++++++--
include/linux/console_struct.h | 3 +++
include/linux/tty.h | 1 +
6 files changed, 45 insertions(+), 18 deletions(-)

diff --git a/drivers/char/keyboard.c b/drivers/char/keyboard.c
index 7a6c1c0..c654a3e 100644
--- 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 05810c8..6cf877f 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -61,9 +61,9 @@ 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 4044c86..a333881 100644
--- 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
@@ -3399,6 +3397,13 @@ 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,
@@ -3409,7 +3414,7 @@ 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 311493e..8384846 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 +1064,35 @@ 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 ed6c0fe..a86162b 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 65cbcf2..0161a8c 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);
--
1.4.4.1.g278f
-
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