Commit 8b6312f4 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by Linus Torvalds
Browse files

[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: default avatarEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0a7b35cb

drivers/char/keyboard.c

+3 −9
Original line number Diff line number Diff line
@@ -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)

drivers/char/sysrq.c

+3 −3
Original line number Diff line number Diff line
@@ -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,

drivers/char/tty_io.c

+9 −4
Original line number Diff line number Diff line
@@ -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);

}

drivers/char/vt_ioctl.c

+26 −2
Original line number Diff line number Diff line
@@ -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

 */

include/linux/console_struct.h

+3 −0
Original line number Diff line number Diff line
@@ -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

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