From 06181de14ff09b274b699ee2dd39fe5e37efb419 Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Wed, 18 Nov 2015 17:55:04 +0000 Subject: [PATCH] staging: comedi: rearrange comedi_write() code Rearrange the code in `comedi_write()` to reduce the amount of indentation. The code never reiterates the `while` loop once `count` has become non-zero, so we can check that in the `while` condition to save an indentation level. (Note that `nbytes` has been checked to be non-zero before entering the loop, so we can remove that check.) Move the code that makes the subdevice "become non-busy" outside the `while` loop, using a new flag variable `become_nonbusy` to decide whether it needs to be done. This simplifies the wait queue handling so there is a single place where the task is removed from the wait queue, and we can remove the `on_wait_queue` flag variable. Signed-off-by: Ian Abbott Reviewed-by: H Hartley Sweeten Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/comedi_fops.c | 71 ++++++++++++---------------- 1 file changed, 30 insertions(+), 41 deletions(-) diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c index 7b4af519e17e..c9da6f39b1c6 100644 --- a/drivers/staging/comedi/comedi_fops.c +++ b/drivers/staging/comedi/comedi_fops.c @@ -2307,7 +2307,7 @@ static ssize_t comedi_write(struct file *file, const char __user *buf, DECLARE_WAITQUEUE(wait, current); struct comedi_file *cfp = file->private_data; struct comedi_device *dev = cfp->dev; - bool on_wait_queue = false; + bool become_nonbusy = false; bool attach_locked; unsigned int old_detach_count; @@ -2342,48 +2342,16 @@ static ssize_t comedi_write(struct file *file, const char __user *buf, } add_wait_queue(&async->wait_head, &wait); - on_wait_queue = true; - while (nbytes > 0 && !retval) { + while (count == 0 && !retval) { unsigned runflags; set_current_state(TASK_INTERRUPTIBLE); runflags = comedi_get_subdevice_runflags(s); if (!comedi_is_runflags_running(runflags)) { - if (count == 0) { - struct comedi_subdevice *new_s; - - if (comedi_is_runflags_in_error(runflags)) - retval = -EPIPE; - else - retval = 0; - /* - * To avoid deadlock, cannot acquire dev->mutex - * while dev->attach_lock is held. Need to - * remove task from the async wait queue before - * releasing dev->attach_lock, as it might not - * be valid afterwards. - */ - remove_wait_queue(&async->wait_head, &wait); - on_wait_queue = false; - up_read(&dev->attach_lock); - attach_locked = false; - mutex_lock(&dev->mutex); - /* - * Become non-busy unless things have changed - * behind our back. Checking dev->detach_count - * is unchanged ought to be sufficient (unless - * there have been 2**32 detaches in the - * meantime!), but check the subdevice pointer - * as well just in case. - */ - new_s = comedi_file_write_subdevice(file); - if (dev->attached && - old_detach_count == dev->detach_count && - s == new_s && new_s->async == async) - do_become_nonbusy(dev, s); - mutex_unlock(&dev->mutex); - } + if (comedi_is_runflags_in_error(runflags)) + retval = -EPIPE; + become_nonbusy = true; break; } @@ -2433,12 +2401,33 @@ static ssize_t comedi_write(struct file *file, const char __user *buf, nbytes -= n; buf += n; - break; /* makes device work like a pipe */ } -out: - if (on_wait_queue) - remove_wait_queue(&async->wait_head, &wait); + remove_wait_queue(&async->wait_head, &wait); set_current_state(TASK_RUNNING); + if (become_nonbusy && count == 0) { + struct comedi_subdevice *new_s; + + /* + * To avoid deadlock, cannot acquire dev->mutex + * while dev->attach_lock is held. + */ + up_read(&dev->attach_lock); + attach_locked = false; + mutex_lock(&dev->mutex); + /* + * Check device hasn't become detached behind our back. + * Checking dev->detach_count is unchanged ought to be + * sufficient (unless there have been 2**32 detaches in the + * meantime!), but check the subdevice pointer as well just in + * case. + */ + new_s = comedi_file_write_subdevice(file); + if (dev->attached && old_detach_count == dev->detach_count && + s == new_s && new_s->async == async) + do_become_nonbusy(dev, s); + mutex_unlock(&dev->mutex); + } +out: if (attach_locked) up_read(&dev->attach_lock); -- 2.20.1