Re: n_tty_read panic

[Stanislav Kozina <skozina@redhat.com>]

Seems that tty->read_buf == NULL at the very beginning of n_tty_read():

1723 do_it_again:
1724
1725         BUG_ON(!tty->read_buf);

tty->read_buf access needs tty->read_lock to be held, correct? So 
perhaps the patch would be:

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index ee1c268..9decb1c 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1728,7 +1728,11 @@ static ssize_t n_tty_read(struct tty_struct *tty, 
struct file *file,

  do_it_again:

+#ifdef CONFIG_BUG
+       spin_lock_irqsave(&tty->read_lock, flags);
         BUG_ON(!tty->read_buf);
+       spin_unlock_irqrestore(&tty->read_lock, flags);
+#endif

         c = job_control(tty, file);
         if (c < 0)

Regards,
-Stanislav Kozina

> On Wed, 25 Jul 2012 09:47:09 +0800
> "大林"<yourdarling1999@sina.com>  wrote:
>
>> Hello.
>>
>> Here's a kernel panic caused by n_tty_read, linux kernel version is 2.6.38.8.
>>
>>
>> There are many discussions on the subject, this bug solved yet? Where can I download the patch?
> Thats a different trace to the others I've seen. Several races have been
> fixed, there are certainly a couple of others left to sort eventually. I
> don't believe anyone is currently working on them (and indeed until the
> rest of the locking and lock splitting work is done it's difficult to see
> how any useful progress could be made here). Patches are however welcome.
>
> Alan
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