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    Subject[PATCH] tty: hold lock across tty buffer finding and buffer filling
    Date
    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(-)
    mode change 100644 => 100755 drivers/tty/tty_buffer.c

    diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
    old mode 100644
    new mode 100755
    index 6c9b7cd..6810f2d
    --- 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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