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SubjectRE: [PATCH] tty: hold lock across tty buffer finding and buffer filling
Date
If you really look at the original patch from Xiaobing, the tty_prepare_flip_string is also patched :-)
Actually it fills up all the possible spin_lock gaps in tty_buffer.c


@@ -344,13 +375,20 @@ EXPORT_SYMBOL(tty_schedule_flip); int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
size_t size)
{
- int space = tty_buffer_request_room(tty, size);
+ int space;
+ unsigned long flags;
+ struct tty_buffer *tb;
+
+ spin_lock_irqsave(&tty->buf.lock, flags);
+ space = __tty_buffer_request_room(tty, size);
+
+ tb = tty->buf.tail;
if (likely(space)) {
- struct tty_buffer *tb = tty->buf.tail;
*chars = tb->char_buf_ptr + tb->used;
memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
tb->used += space;
}
+ spin_unlock_irqrestore(&tty->buf.lock, flags);
return space;
}

Thanks,
Alek
-----Original Message-----
From: Jiri Slaby [mailto:jirislaby@gmail.com] On Behalf Of Jiri Slaby
Sent: Friday, March 16, 2012 6:04 PM
To: Du, Alek
Cc: jiris >> Jiri Slaby; Alan Cox; Tu, Xiaobing; linux-kernel@vger.kernel.org; gregkh@linuxfoundation.org; Zhang, Yanmin; Zuo, Jiao
Subject: Re: [PATCH] tty: hold lock across tty buffer finding and buffer filling

On 03/16/2012 11:01 AM, Du, Alek wrote:
> We prepared the buffer, and use it. And during this, we don't release the spinlock of buf.lock, how the flush could happen?
>
> A
> spin_lock
> prepare the buffer
> user the buffer
> spin unlock
>
>
> B
> Spin_lock
> Flush
> Free the buffer
> Put buf.tail = NULL
> Spin unlock

Well, you do. Not all drivers use tty_insert_flip_string. Take a look at tty_prepare_flip_string and its users.

thanks,
--
js
suse labs


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