From 053b47ff249b9e0a634dae807f81465205e7c228 Mon Sep 17 00:00:00 2001 From: Michael Buesch Date: Mon, 12 Feb 2007 00:53:26 -0800 Subject: [PATCH] [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: Michael Buesch Cc: Kai Germaschewski Cc: Karsten Keil Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/isdn/capi/capi.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/drivers/isdn/capi/capi.c b/drivers/isdn/capi/capi.c index 38045910ca94..9e48bb5a3c09 100644 --- a/drivers/isdn/capi/capi.c +++ b/drivers/isdn/capi/capi.c @@ -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); } } -- 2.20.1