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SubjectRE: [PATCH v2] tty: hold lock across tty buffer finding and buffer filling
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Hi Greg
Even there still a prepare buffer not protected, the patch is still good to protect rest case, so this patch is still "nice to have"
it makes the situation better. for the not-fixed case, we can have another patch to address that. Do you agree?

Br
Xiaobing


-----Original Message-----
From: gregkh@linuxfoundation.org [mailto:gregkh@linuxfoundation.org]
Sent: Saturday, March 17, 2012 4:15 AM
To: Tu, Xiaobing; Jiri Slaby
Cc: alan@lxorguk.ukuu.org.uk; linux-kernel@vger.kernel.org; Zhang, Yanmin; Du, Alek; Zuo, Jiao
Subject: Re: [PATCH v2] tty: hold lock across tty buffer finding and buffer filling
Jiri,

Do you have any objections to me applying the patch below?

thanks,

greg k-h

On Fri, Mar 16, 2012 at 03:00:26AM +0000, Tu, Xiaobing wrote:
> From: Xiaobing Tu <xiaobing.tu@intel.com>
> tty_buffer_request_room is well protected, but while after it returns,
> it releases the port->lock. tty->buf.tail might be modified by either
> irq handler or other threads. The patch adds more protection by
> holding the lock across tty buffer finding and buffer filling.
> Signed-off-by: Alek Du <alek.du@intel.com>
> Signed-off-by: Xiaobing Tu <xiaobing.tu@intel.com>
> ---
> drivers/tty/tty_buffer.c | 85 +++++++++++++++++++++++++++++++++++-----------
> 1 files changed, 65 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index
> 6c9b7cd..91e326f 100644
> --- a/drivers/tty/tty_buffer.c
> +++ b/drivers/tty/tty_buffer.c
> @@ -185,25 +185,19 @@ static struct tty_buffer *tty_buffer_find(struct tty_struct *tty, size_t size)
> /* Should possibly check if this fails for the largest buffer we
> have queued and recycle that ? */ }
> -
> /**
> - * tty_buffer_request_room - grow tty buffer if needed
> + * __tty_buffer_request_room - grow tty buffer if needed
> * @tty: tty structure
> * @size: size desired
> *
> * Make at least size bytes of linear space available for the tty
> * buffer. If we fail return the size we managed to find.
> - *
> - * Locking: Takes tty->buf.lock
> + * Locking: Caller must hold tty->buf.lock
> */
> -int tty_buffer_request_room(struct tty_struct *tty, size_t size)
> +static int __tty_buffer_request_room(struct tty_struct *tty, size_t
> +size)
> {
> struct tty_buffer *b, *n;
> int left;
> - unsigned long flags;
> -
> - spin_lock_irqsave(&tty->buf.lock, flags);
> -
> /* OPTIMISATION: We could keep a per tty "zero" sized buffer to
> remove this conditional if its worth it. This would be invisible
> to the callers */
> @@ -225,9 +219,30 @@ int tty_buffer_request_room(struct tty_struct *tty, size_t size)
> size = left;
> }
>
> - spin_unlock_irqrestore(&tty->buf.lock, flags);
> return size;
> }
> +
> +
> +/**
> + * tty_buffer_request_room - grow tty buffer if needed
> + * @tty: tty structure
> + * @size: size desired
> + *
> + * Make at least size bytes of linear space available for the tty
> + * buffer. If we fail return the size we managed to find.
> + *
> + * Locking: Takes tty->buf.lock
> + */
> +int tty_buffer_request_room(struct tty_struct *tty, size_t size) {
> + unsigned long flags;
> + int length;
> +
> + spin_lock_irqsave(&tty->buf.lock, flags);
> + length = __tty_buffer_request_room(tty, size);
> + spin_unlock_irqrestore(&tty->buf.lock, flags);
> + return length;
> +}
> EXPORT_SYMBOL_GPL(tty_buffer_request_room);
>
> /**
> @@ -249,14 +264,22 @@ int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
> int copied = 0;
> do {
> int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
> - int space = tty_buffer_request_room(tty, goal);
> - struct tty_buffer *tb = tty->buf.tail;
> + int space;
> + unsigned long flags;
> + struct tty_buffer *tb;
> +
> + spin_lock_irqsave(&tty->buf.lock, flags);
> + space = __tty_buffer_request_room(tty, goal);
> + tb = tty->buf.tail;
> /* If there is no space then tb may be NULL */
> - if (unlikely(space == 0))
> + if (unlikely(space == 0)) {
> + spin_unlock_irqrestore(&tty->buf.lock, flags);
> break;
> + }
> memcpy(tb->char_buf_ptr + tb->used, chars, space);
> memset(tb->flag_buf_ptr + tb->used, flag, space);
> tb->used += space;
> + spin_unlock_irqrestore(&tty->buf.lock, flags);
> copied += space;
> chars += space;
> /* There is a small chance that we need to split the data over @@
> -286,14 +309,22 @@ int tty_insert_flip_string_flags(struct tty_struct *tty,
> int copied = 0;
> do {
> int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
> - int space = tty_buffer_request_room(tty, goal);
> - struct tty_buffer *tb = tty->buf.tail;
> + int space;
> + unsigned long __flags;
> + struct tty_buffer *tb;
> +
> + spin_lock_irqsave(&tty->buf.lock, __flags);
> + space = __tty_buffer_request_room(tty, goal);
> + tb = tty->buf.tail;
> /* If there is no space then tb may be NULL */
> - if (unlikely(space == 0))
> + if (unlikely(space == 0)) {
> + spin_unlock_irqrestore(&tty->buf.lock, __flags);
> break;
> + }
> memcpy(tb->char_buf_ptr + tb->used, chars, space);
> memcpy(tb->flag_buf_ptr + tb->used, flags, space);
> tb->used += space;
> + spin_unlock_irqrestore(&tty->buf.lock, __flags);
> copied += space;
> chars += space;
> flags += space;
> @@ -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;
> }
> EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
> @@ -374,13 +412,20 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
> int tty_prepare_flip_string_flags(struct tty_struct *tty,
> unsigned char **chars, char **flags, 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;
> *flags = tb->flag_buf_ptr + tb->used;
> tb->used += space;
> }
> + spin_unlock_irqrestore(&tty->buf.lock, __flags);
> return space;
> }
> EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
> --
> 1.7.4.1


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