From e74d098c66543d0731de62eb747ccd5b636a6f4c Mon Sep 17 00:00:00 2001 From: Amit Shah Date: Fri, 12 Mar 2010 11:53:15 +0530 Subject: [PATCH] hvc_console: Fix race between hvc_close and hvc_remove Alan pointed out a race in the code where hvc_remove is invoked. The recent virtio_console work is the first user of hvc_remove(). Alan describes it thus: The hvc_console assumes that a close and remove call can't occur at the same time. In addition tty_hangup(tty) is problematic as tty_hangup is asynchronous itself.... So this can happen hvc_close hvc_remove hung up ? - no lock tty = hp->tty unlock lock hp->tty = NULL unlock notify del kref_put the hvc struct close completes tty is destroyed tty_hangup dead tty tty->ops will be NULL NULL->... This patch adds some tty krefs and also converts to using tty_vhangup(). Reported-by: Alan Cox Signed-off-by: Amit Shah CC: Alan Cox CC: linuxppc-dev@ozlabs.org CC: Rusty Russell Signed-off-by: Greg Kroah-Hartman --- drivers/char/hvc_console.c | 31 +++++++++++++++++++++---------- 1 file changed, 21 insertions(+), 10 deletions(-) diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index 465185fc0f52..ba55bba151b9 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -312,6 +312,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) spin_lock_irqsave(&hp->lock, flags); /* Check and then increment for fast path open. */ if (hp->count++ > 0) { + tty_kref_get(tty); spin_unlock_irqrestore(&hp->lock, flags); hvc_kick(); return 0; @@ -319,7 +320,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) tty->driver_data = hp; - hp->tty = tty; + hp->tty = tty_kref_get(tty); spin_unlock_irqrestore(&hp->lock, flags); @@ -336,6 +337,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) spin_lock_irqsave(&hp->lock, flags); hp->tty = NULL; spin_unlock_irqrestore(&hp->lock, flags); + tty_kref_put(tty); tty->driver_data = NULL; kref_put(&hp->kref, destroy_hvc_struct); printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc); @@ -363,13 +365,18 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) return; hp = tty->driver_data; + spin_lock_irqsave(&hp->lock, flags); + tty_kref_get(tty); if (--hp->count == 0) { /* We are done with the tty pointer now. */ hp->tty = NULL; spin_unlock_irqrestore(&hp->lock, flags); + /* Put the ref obtained in hvc_open() */ + tty_kref_put(tty); + if (hp->ops->notifier_del) hp->ops->notifier_del(hp, hp->data); @@ -389,6 +396,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) spin_unlock_irqrestore(&hp->lock, flags); } + tty_kref_put(tty); kref_put(&hp->kref, destroy_hvc_struct); } @@ -424,10 +432,11 @@ static void hvc_hangup(struct tty_struct *tty) spin_unlock_irqrestore(&hp->lock, flags); if (hp->ops->notifier_hangup) - hp->ops->notifier_hangup(hp, hp->data); + hp->ops->notifier_hangup(hp, hp->data); while(temp_open_count) { --temp_open_count; + tty_kref_put(tty); kref_put(&hp->kref, destroy_hvc_struct); } } @@ -592,7 +601,7 @@ int hvc_poll(struct hvc_struct *hp) } /* No tty attached, just skip */ - tty = hp->tty; + tty = tty_kref_get(hp->tty); if (tty == NULL) goto bail; @@ -672,6 +681,8 @@ int hvc_poll(struct hvc_struct *hp) tty_flip_buffer_push(tty); } + if (tty) + tty_kref_put(tty); return poll_mask; } @@ -807,7 +818,7 @@ int hvc_remove(struct hvc_struct *hp) struct tty_struct *tty; spin_lock_irqsave(&hp->lock, flags); - tty = hp->tty; + tty = tty_kref_get(hp->tty); if (hp->index < MAX_NR_HVC_CONSOLES) vtermnos[hp->index] = -1; @@ -819,18 +830,18 @@ int hvc_remove(struct hvc_struct *hp) /* * We 'put' the instance that was grabbed when the kref instance * was initialized using kref_init(). Let the last holder of this - * kref cause it to be removed, which will probably be the tty_hangup + * kref cause it to be removed, which will probably be the tty_vhangup * below. */ kref_put(&hp->kref, destroy_hvc_struct); /* - * This function call will auto chain call hvc_hangup. The tty should - * always be valid at this time unless a simultaneous tty close already - * cleaned up the hvc_struct. + * This function call will auto chain call hvc_hangup. */ - if (tty) - tty_hangup(tty); + if (tty) { + tty_vhangup(tty); + tty_kref_put(tty); + } return 0; } EXPORT_SYMBOL_GPL(hvc_remove); -- 2.20.1