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hvc_console: Fix race between hvc_close and hvc_remove

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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 <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: linuxppc-dev@ozlabs.org
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Amit Shah 2010-03-12 11:53:15 +05:30 committed by Greg Kroah-Hartman
parent f157b58511
commit e74d098c66
1 changed files with 21 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
drivers/char/hvc_console.c
View File

@ -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);