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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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