From 45242006e19c6f99945554e4d7d5680caf6ed9ad Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Wed, 14 Oct 2009 08:59:49 -0700 Subject: [PATCH 1/3] Make flush_to_ldisc properly handle parallel calls --- drivers/char/tty_buffer.c | 29 +++++++++++++---------------- 1 file changed, 13 insertions(+), 16 deletions(-) diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c index 3108991c5c8b..0296612cc7df 100644 --- a/drivers/char/tty_buffer.c +++ b/drivers/char/tty_buffer.c @@ -402,28 +402,26 @@ static void flush_to_ldisc(struct work_struct *work) container_of(work, struct tty_struct, buf.work.work); unsigned long flags; struct tty_ldisc *disc; - struct tty_buffer *tbuf, *head; - char *char_buf; - unsigned char *flag_buf; disc = tty_ldisc_ref(tty); if (disc == NULL) /* !TTY_LDISC */ return; spin_lock_irqsave(&tty->buf.lock, flags); - /* So we know a flush is running */ - set_bit(TTY_FLUSHING, &tty->flags); - head = tty->buf.head; - if (head != NULL) { - tty->buf.head = NULL; - for (;;) { - int count = head->commit - head->read; + + if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) { + struct tty_buffer *head; + while ((head = tty->buf.head) != NULL) { + int count; + char *char_buf; + unsigned char *flag_buf; + + count = head->commit - head->read; if (!count) { if (head->next == NULL) break; - tbuf = head; - head = head->next; - tty_buffer_free(tty, tbuf); + tty->buf.head = head->next; + tty_buffer_free(tty, head); continue; } /* Ldisc or user is trying to flush the buffers @@ -445,9 +443,9 @@ static void flush_to_ldisc(struct work_struct *work) flag_buf, count); spin_lock_irqsave(&tty->buf.lock, flags); } - /* Restore the queue head */ - tty->buf.head = head; + clear_bit(TTY_FLUSHING, &tty->flags); } + /* We may have a deferred request to flush the input buffer, if so pull the chain under the lock and empty the queue */ if (test_bit(TTY_FLUSHPENDING, &tty->flags)) { @@ -455,7 +453,6 @@ static void flush_to_ldisc(struct work_struct *work) clear_bit(TTY_FLUSHPENDING, &tty->flags); wake_up(&tty->read_wait); } - clear_bit(TTY_FLUSHING, &tty->flags); spin_unlock_irqrestore(&tty->buf.lock, flags); tty_ldisc_deref(disc); From 43046b606673c9c991919ff75b980b72541e9ede Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Wed, 14 Oct 2009 09:16:42 -0700 Subject: [PATCH 2/3] workqueue: add 'flush_delayed_work()' to run and wait for delayed work It basically turns a delayed work into an immediate work, and then waits for it to finish. --- include/linux/workqueue.h | 1 + kernel/workqueue.c | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+) diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 7ef0c7b94f31..cf24c20de9e4 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -207,6 +207,7 @@ extern int queue_delayed_work_on(int cpu, struct workqueue_struct *wq, extern void flush_workqueue(struct workqueue_struct *wq); extern void flush_scheduled_work(void); +extern void flush_delayed_work(struct delayed_work *work); extern int schedule_work(struct work_struct *work); extern int schedule_work_on(int cpu, struct work_struct *work); diff --git a/kernel/workqueue.c b/kernel/workqueue.c index addfe2df93b1..ccefe574dcf7 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -639,6 +639,24 @@ int schedule_delayed_work(struct delayed_work *dwork, } EXPORT_SYMBOL(schedule_delayed_work); +/** + * flush_delayed_work - block until a dwork_struct's callback has terminated + * @dwork: the delayed work which is to be flushed + * + * Any timeout is cancelled, and any pending work is run immediately. + */ +void flush_delayed_work(struct delayed_work *dwork) +{ + if (del_timer(&dwork->timer)) { + struct cpu_workqueue_struct *cwq; + cwq = wq_per_cpu(keventd_wq, get_cpu()); + __queue_work(cwq, &dwork->work); + put_cpu(); + } + flush_work(&dwork->work); +} +EXPORT_SYMBOL(flush_delayed_work); + /** * schedule_delayed_work_on - queue work in global workqueue on CPU after delay * @cpu: cpu to use From 514fc01d389cf5d364ee3b5fec4ac1487448803e Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Wed, 14 Oct 2009 09:20:41 -0700 Subject: [PATCH 3/3] tty: use the new 'flush_delayed_work()' helper to do ldisc flush This way all flush_to_ldisc work is always done through the workqueues, and we thus have a single point of serialization. Signed-off-by: Linus Torvalds --- drivers/char/tty_buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c index 0296612cc7df..66fa4e10d76b 100644 --- a/drivers/char/tty_buffer.c +++ b/drivers/char/tty_buffer.c @@ -468,7 +468,7 @@ static void flush_to_ldisc(struct work_struct *work) */ void tty_flush_to_ldisc(struct tty_struct *tty) { - flush_to_ldisc(&tty->buf.work.work); + flush_delayed_work(&tty->buf.work); } /**