Commit 053b47ff authored by Michael Buesch's avatar Michael Buesch Committed by Linus Torvalds
Browse files

[PATCH] Workaround CAPI subsystem locking issue 



I think the following patch should go into the kernel, until the ISDN/CAPI
guys create the real fix for this issue.

The issue is a concurrency issue with some internal CAPI data structure
which can crash the kernel.

On my FritzCard DSL with the AVM driver it crashes about once a day without
this workaround patch.  With this workaround patch it's rock-stable (at
least on UP, but I don't see why this shouldn't work on SMP as well.  But
maybe I'm missing something.)

This workaround is kind of a sledgehammer which inserts a global lock to
wrap around all the critical sections.  Of course, this is a scalability
issue, if you have many ISDN/CAPI cards.  But it prevents a crash.  So I
vote for this fix to get merged, until people come up with a better
solution.  Better have a stable kernel that's less scalable, than a
crashing and useless kernel.

This bug is in the kernel since 2.6.15 (at least).

Signed-off-by: default avatarMichael Buesch <mb@bu3sch.de>
Cc: Kai Germaschewski <kai.germaschewski@gmx.de>
Cc: Karsten Keil <kkeil@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a871fe85

drivers/isdn/capi/capi.c

+35 −0
Original line number Diff line number Diff line
@@ -118,6 +118,15 @@ struct capiminor { 
};

#endif /* CONFIG_ISDN_CAPI_MIDDLEWARE */



/* FIXME: The following lock is a sledgehammer-workaround to a

 * locking issue with the capiminor (and maybe other) data structure(s).

 * Access to this data is done in a racy way and crashes the machine with

 * a FritzCard DSL driver; sooner or later. This is a workaround

 * which trades scalability vs stability, so it doesn't crash the kernel anymore.

 * The correct (and scalable) fix for the issue seems to require

 * an API change to the drivers... . */

static DEFINE_SPINLOCK(workaround_lock);



struct capincci {

	struct capincci *next;

	u32		 ncci;
@@ -589,6 +598,7 @@ static void capi_recv_message(struct capi20_appl *ap, struct sk_buff *skb) 
#endif /* CONFIG_ISDN_CAPI_MIDDLEWARE */

	struct capincci *np;

	u32 ncci;

	unsigned long flags;



	if (CAPIMSG_CMD(skb->data) == CAPI_CONNECT_B3_CONF) {

		u16 info = CAPIMSG_U16(skb->data, 12); // Info field
@@ -603,9 +613,11 @@ static void capi_recv_message(struct capi20_appl *ap, struct sk_buff *skb) 
		capincci_alloc(cdev, CAPIMSG_NCCI(skb->data));

		up(&cdev->ncci_list_sem);

	}

	spin_lock_irqsave(&workaround_lock, flags);

	if (CAPIMSG_COMMAND(skb->data) != CAPI_DATA_B3) {

		skb_queue_tail(&cdev->recvqueue, skb);

		wake_up_interruptible(&cdev->recvwait);

		spin_unlock_irqrestore(&workaround_lock, flags);

		return;

	}

	ncci = CAPIMSG_CONTROL(skb->data);
@@ -615,6 +627,7 @@ static void capi_recv_message(struct capi20_appl *ap, struct sk_buff *skb) 
		printk(KERN_ERR "BUG: capi_signal: ncci not found\n");

		skb_queue_tail(&cdev->recvqueue, skb);

		wake_up_interruptible(&cdev->recvwait);

		spin_unlock_irqrestore(&workaround_lock, flags);

		return;

	}

#ifndef CONFIG_ISDN_CAPI_MIDDLEWARE
@@ -625,6 +638,7 @@ static void capi_recv_message(struct capi20_appl *ap, struct sk_buff *skb) 
	if (!mp) {

		skb_queue_tail(&cdev->recvqueue, skb);

		wake_up_interruptible(&cdev->recvwait);

		spin_unlock_irqrestore(&workaround_lock, flags);

		return;

	}
@@ -660,6 +674,7 @@ static void capi_recv_message(struct capi20_appl *ap, struct sk_buff *skb) 
		wake_up_interruptible(&cdev->recvwait);

	}

#endif /* CONFIG_ISDN_CAPI_MIDDLEWARE */

	spin_unlock_irqrestore(&workaround_lock, flags);

}



/* -------- file_operations for capidev ----------------------------- */
@@ -1006,6 +1021,7 @@ static struct file_operations capi_fops = 
static int capinc_tty_open(struct tty_struct * tty, struct file * file)

{

	struct capiminor *mp;

	unsigned long flags;



	if ((mp = capiminor_find(iminor(file->f_path.dentry->d_inode))) == 0)

		return -ENXIO;
@@ -1014,6 +1030,7 @@ static int capinc_tty_open(struct tty_struct * tty, struct file * file) 


	tty->driver_data = (void *)mp;



	spin_lock_irqsave(&workaround_lock, flags);

	if (atomic_read(&mp->ttyopencount) == 0)

		mp->tty = tty;

	atomic_inc(&mp->ttyopencount);
@@ -1021,6 +1038,7 @@ static int capinc_tty_open(struct tty_struct * tty, struct file * file) 
	printk(KERN_DEBUG "capinc_tty_open ocount=%d\n", atomic_read(&mp->ttyopencount));

#endif

	handle_minor_recv(mp);

	spin_unlock_irqrestore(&workaround_lock, flags);

	return 0;

}
@@ -1054,6 +1072,7 @@ static int capinc_tty_write(struct tty_struct * tty, 
{

	struct capiminor *mp = (struct capiminor *)tty->driver_data;

	struct sk_buff *skb;

	unsigned long flags;



#ifdef _DEBUG_TTYFUNCS

	printk(KERN_DEBUG "capinc_tty_write(count=%d)\n", count);
@@ -1066,6 +1085,7 @@ static int capinc_tty_write(struct tty_struct * tty, 
		return 0;

	}



	spin_lock_irqsave(&workaround_lock, flags);

	skb = mp->ttyskb;

	if (skb) {

		mp->ttyskb = NULL;
@@ -1076,6 +1096,7 @@ static int capinc_tty_write(struct tty_struct * tty, 
	skb = alloc_skb(CAPI_DATA_B3_REQ_LEN+count, GFP_ATOMIC);

	if (!skb) {

		printk(KERN_ERR "capinc_tty_write: alloc_skb failed\n");

		spin_unlock_irqrestore(&workaround_lock, flags);

		return -ENOMEM;

	}
@@ -1086,6 +1107,7 @@ static int capinc_tty_write(struct tty_struct * tty, 
	mp->outbytes += skb->len;

	(void)handle_minor_send(mp);

	(void)handle_minor_recv(mp);

	spin_unlock_irqrestore(&workaround_lock, flags);

	return count;

}
@@ -1093,6 +1115,7 @@ static void capinc_tty_put_char(struct tty_struct *tty, unsigned char ch) 
{

	struct capiminor *mp = (struct capiminor *)tty->driver_data;

	struct sk_buff *skb;

	unsigned long flags;



#ifdef _DEBUG_TTYFUNCS

	printk(KERN_DEBUG "capinc_put_char(%u)\n", ch);
@@ -1105,10 +1128,12 @@ static void capinc_tty_put_char(struct tty_struct *tty, unsigned char ch) 
		return;

	}



	spin_lock_irqsave(&workaround_lock, flags);

	skb = mp->ttyskb;

	if (skb) {

		if (skb_tailroom(skb) > 0) {

			*(skb_put(skb, 1)) = ch;

			spin_unlock_irqrestore(&workaround_lock, flags);

			return;

		}

		mp->ttyskb = NULL;
@@ -1124,12 +1149,14 @@ static void capinc_tty_put_char(struct tty_struct *tty, unsigned char ch) 
	} else {

		printk(KERN_ERR "capinc_put_char: char %u lost\n", ch);

	}

	spin_unlock_irqrestore(&workaround_lock, flags);

}



static void capinc_tty_flush_chars(struct tty_struct *tty)

{

	struct capiminor *mp = (struct capiminor *)tty->driver_data;

	struct sk_buff *skb;

	unsigned long flags;



#ifdef _DEBUG_TTYFUNCS

	printk(KERN_DEBUG "capinc_tty_flush_chars\n");
@@ -1142,6 +1169,7 @@ static void capinc_tty_flush_chars(struct tty_struct *tty) 
		return;

	}



	spin_lock_irqsave(&workaround_lock, flags);

	skb = mp->ttyskb;

	if (skb) {

		mp->ttyskb = NULL;
@@ -1150,6 +1178,7 @@ static void capinc_tty_flush_chars(struct tty_struct *tty) 
		(void)handle_minor_send(mp);

	}

	(void)handle_minor_recv(mp);

	spin_unlock_irqrestore(&workaround_lock, flags);

}



static int capinc_tty_write_room(struct tty_struct *tty)
@@ -1220,12 +1249,15 @@ static void capinc_tty_throttle(struct tty_struct * tty) 
static void capinc_tty_unthrottle(struct tty_struct * tty)

{

	struct capiminor *mp = (struct capiminor *)tty->driver_data;

	unsigned long flags;

#ifdef _DEBUG_TTYFUNCS

	printk(KERN_DEBUG "capinc_tty_unthrottle\n");

#endif

	if (mp) {

		spin_lock_irqsave(&workaround_lock, flags);

		mp->ttyinstop = 0;

		handle_minor_recv(mp);

		spin_unlock_irqrestore(&workaround_lock, flags);

	}

}
@@ -1243,12 +1275,15 @@ static void capinc_tty_stop(struct tty_struct *tty) 
static void capinc_tty_start(struct tty_struct *tty)

{

	struct capiminor *mp = (struct capiminor *)tty->driver_data;

	unsigned long flags;

#ifdef _DEBUG_TTYFUNCS

	printk(KERN_DEBUG "capinc_tty_start\n");

#endif

	if (mp) {

		spin_lock_irqsave(&workaround_lock, flags);

		mp->ttyoutstop = 0;

		(void)handle_minor_send(mp);

		spin_unlock_irqrestore(&workaround_lock, flags);

	}

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE