| Submitter | Amit Shah |
|---|---|
| Date | Feb. 26, 2010, 11:46 a.m. |
| Message ID | <1267184786-4377-1-git-send-email-amit.shah@redhat.com> |
| Download | mbox | patch |
| Permalink | /patch/46323/ |
| State | Not Applicable |
| Headers | show |
Comments
> + tty_kref_get(hp->tty); > spin_lock_irqsave(&hp->lock, flags); > tty = hp->tty; > > @@ -830,7 +833,9 @@ int hvc_remove(struct hvc_struct *hp) > * cleaned up the hvc_struct. > */ > if (tty) > - tty_hangup(tty); > + tty_vhangup(tty); > + > + tty_kref_put(hp->tty); You need to deref hp->tty, take the kref under the lock (and indeed do all assignments to it that way too), then tty_kref_put(tty), otherwise what stops hp->tty changing during the remove ? Take a look how tty_port_tty_get() and tty_port.c does it ... Alan
Patch
diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c index d8dac58..3983e32 100644 --- a/drivers/char/hvc_console.c +++ b/drivers/char/hvc_console.c @@ -106,6 +106,7 @@ static struct hvc_struct *hvc_get_by_index(int index) spin_lock_irqsave(&hp->lock, flags); if (hp->index == index) { kref_get(&hp->kref); + tty_kref_get(hp->tty); spin_unlock_irqrestore(&hp->lock, flags); spin_unlock(&hvc_structs_lock); return hp; @@ -390,6 +391,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) } kref_put(&hp->kref, destroy_hvc_struct); + tty_kref_put(tty); } static void hvc_hangup(struct tty_struct *tty) @@ -806,6 +808,7 @@ int hvc_remove(struct hvc_struct *hp) unsigned long flags; struct tty_struct *tty; + tty_kref_get(hp->tty); spin_lock_irqsave(&hp->lock, flags); tty = hp->tty; @@ -830,7 +833,9 @@ int hvc_remove(struct hvc_struct *hp) * cleaned up the hvc_struct. */ if (tty) - tty_hangup(tty); + tty_vhangup(tty); + + tty_kref_put(hp->tty); return 0; } EXPORT_SYMBOL_GPL(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() before putting the tty kref. 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> --- I can't be sure if this is all that's needed. tty people, please take a look! drivers/char/hvc_console.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-)