Revert "tty: Fix race condition between __tty_buffer_request_room and flush_to_ldisc"
This reverts commit 6a20dbd6caa2358716136144bf524331d70b1e03.
Although the commit correctly identifies an unsafe race condition
between __tty_buffer_request_room() and flush_to_ldisc(), the commit
fixes the race with an unnecessary spinlock in a lockless algorithm.
The follow-on commit, "tty: Fix lockless tty buffer race" fixes
the race locklessly.
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index f1d30f6..8ebd9f8 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -255,16 +255,11 @@
if (change || left < size) {
/* This is the slow path - looking for new buffers to use */
if ((n = tty_buffer_alloc(port, size)) != NULL) {
- unsigned long iflags;
-
n->flags = flags;
buf->tail = n;
-
- spin_lock_irqsave(&buf->flush_lock, iflags);
b->commit = b->used;
+ smp_mb();
b->next = n;
- spin_unlock_irqrestore(&buf->flush_lock, iflags);
-
} else if (change)
size = 0;
else
@@ -448,7 +443,6 @@
mutex_lock(&buf->lock);
while (1) {
- unsigned long flags;
struct tty_buffer *head = buf->head;
int count;
@@ -456,19 +450,14 @@
if (atomic_read(&buf->priority))
break;
- spin_lock_irqsave(&buf->flush_lock, flags);
count = head->commit - head->read;
if (!count) {
- if (head->next == NULL) {
- spin_unlock_irqrestore(&buf->flush_lock, flags);
+ if (head->next == NULL)
break;
- }
buf->head = head->next;
- spin_unlock_irqrestore(&buf->flush_lock, flags);
tty_buffer_free(port, head);
continue;
}
- spin_unlock_irqrestore(&buf->flush_lock, flags);
count = receive_buf(tty, head, count);
if (!count)
@@ -523,7 +512,6 @@
struct tty_bufhead *buf = &port->buf;
mutex_init(&buf->lock);
- spin_lock_init(&buf->flush_lock);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 036cccd..1c3316a 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -61,7 +61,6 @@
struct tty_buffer *head; /* Queue head */
struct work_struct work;
struct mutex lock;
- spinlock_t flush_lock;
atomic_t priority;
struct tty_buffer sentinel;
struct llist_head free; /* Free queue head */
