Use a 0-sized sentinel to avoid assigning the head ptr from the driver side thread. This also eliminates testing head/tail for NULL.
When the sentinel is first 'consumed' by the buffer work (or by tty_buffer_flush()), it is detached from the list but not freed nor added to the free list. Both buffer work and tty_buffer_flush() continue to preserve at least 1 flip buffer to which head & tail is pointed. Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/tty_buffer.c | 49 ++++++++++++++++++------------------------------ include/linux/tty.h | 1 + 2 files changed, 19 insertions(+), 31 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 069640e..231b7a8 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -49,13 +49,16 @@ void tty_buffer_free_all(struct tty_port *port) while ((p = buf->head) != NULL) { buf->head = p->next; - kfree(p); + if (p->size > 0) + kfree(p); } llist = llist_del_all(&buf->free); llist_for_each_entry_safe(p, next, llist, free) kfree(p); - buf->tail = NULL; + tty_buffer_reset(&buf->sentinel, 0); + buf->head = &buf->sentinel; + buf->tail = &buf->sentinel; buf->memory_used = 0; } @@ -120,7 +123,7 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b) if (b->size > MIN_TTYB_SIZE) kfree(b); - else + else if (b->size > 0) llist_add(&b->free, &buf->free); } @@ -140,8 +143,6 @@ static void __tty_buffer_flush(struct tty_port *port) struct tty_bufhead *buf = &port->buf; struct tty_buffer *next; - if (unlikely(buf->head == NULL)) - return; while ((next = buf->head->next) != NULL) { tty_buffer_free(port, buf->head); buf->head = next; @@ -200,23 +201,14 @@ int tty_buffer_request_room(struct tty_port *port, size_t size) int left; unsigned long flags; spin_lock_irqsave(&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 */ b = buf->tail; - if (b != NULL) - left = b->size - b->used; - else - left = 0; + left = b->size - b->used; if (left < size) { /* This is the slow path - looking for new buffers to use */ if ((n = tty_buffer_alloc(port, size)) != NULL) { - if (b != NULL) { - b->next = n; - b->commit = b->used; - } else - buf->head = n; + b->next = n; + b->commit = b->used; buf->tail = n; } else size = left; @@ -247,10 +239,8 @@ int tty_insert_flip_string_fixed_flag(struct tty_port *port, int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); int space = tty_buffer_request_room(port, goal); struct tty_buffer *tb = port->buf.tail; - /* If there is no space then tb may be NULL */ - if (unlikely(space == 0)) { + if (unlikely(space == 0)) break; - } memcpy(char_buf_ptr(tb, tb->used), chars, space); memset(flag_buf_ptr(tb, tb->used), flag, space); tb->used += space; @@ -285,10 +275,8 @@ int tty_insert_flip_string_flags(struct tty_port *port, int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); int space = tty_buffer_request_room(port, goal); struct tty_buffer *tb = port->buf.tail; - /* If there is no space then tb may be NULL */ - if (unlikely(space == 0)) { + if (unlikely(space == 0)) break; - } memcpy(char_buf_ptr(tb, tb->used), chars, space); memcpy(flag_buf_ptr(tb, tb->used), flags, space); tb->used += space; @@ -322,8 +310,7 @@ void tty_schedule_flip(struct tty_port *port) WARN_ON(port->low_latency); spin_lock_irqsave(&buf->lock, flags); - if (buf->tail != NULL) - buf->tail->commit = buf->tail->used; + buf->tail->commit = buf->tail->used; spin_unlock_irqrestore(&buf->lock, flags); schedule_work(&buf->work); } @@ -438,8 +425,8 @@ static void flush_to_ldisc(struct work_struct *work) spin_lock_irqsave(&buf->lock, flags); if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) { - struct tty_buffer *head; - while ((head = buf->head) != NULL) { + while (1) { + struct tty_buffer *head = buf->head; int count; count = head->commit - head->read; @@ -509,8 +496,7 @@ void tty_flip_buffer_push(struct tty_port *port) unsigned long flags; spin_lock_irqsave(&buf->lock, flags); - if (buf->tail != NULL) - buf->tail->commit = buf->tail->used; + buf->tail->commit = buf->tail->used; spin_unlock_irqrestore(&buf->lock, flags); if (port->low_latency) @@ -535,8 +521,9 @@ void tty_buffer_init(struct tty_port *port) struct tty_bufhead *buf = &port->buf; spin_lock_init(&buf->lock); - buf->head = NULL; - buf->tail = NULL; + tty_buffer_reset(&buf->sentinel, 0); + buf->head = &buf->sentinel; + buf->tail = &buf->sentinel; init_llist_head(&buf->free); buf->memory_used = 0; INIT_WORK(&buf->work, flush_to_ldisc); diff --git a/include/linux/tty.h b/include/linux/tty.h index a01fda7..5fe2f68 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -67,6 +67,7 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs) struct tty_bufhead { struct work_struct work; spinlock_t lock; + struct tty_buffer sentinel; struct tty_buffer *head; /* Queue head */ struct tty_buffer *tail; /* Active buffer */ struct llist_head free; /* Free queue head */ -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
