Commit fcf68f3c authored Aug 08, 2016 by Brian Norris Committed by Jonathan Cameron Aug 21, 2016

iio: fix sched WARNING "do not call blocking ops when !TASK_RUNNING"

When using CONFIG_DEBUG_ATOMIC_SLEEP, the scheduler nicely points out
that we're calling sleeping primitives within the wait_event loop, which
means we might clobber the task state:

[   10.831289] do not call blocking ops when !TASK_RUNNING; state=1 set at [<ffffffc00026b610>]
[   10.845531] ------------[ cut here ]------------
[   10.850161] WARNING: at kernel/sched/core.c:7630
...
[   12.164333] ---[ end trace 45409966a9a76438 ]---
[   12.168942] Call trace:
[   12.171391] [<ffffffc00024ed44>] __might_sleep+0x64/0x90
[   12.176699] [<ffffffc000954774>] mutex_lock_nested+0x50/0x3fc
[   12.182440] [<ffffffc0007b9424>] iio_kfifo_buf_data_available+0x28/0x4c
[   12.189043] [<ffffffc0007b76ac>] iio_buffer_ready+0x60/0xe0
[   12.194608] [<ffffffc0007b7834>] iio_buffer_read_first_n_outer+0x108/0x1a8
[   12.201474] [<ffffffc000370d48>] __vfs_read+0x58/0x114
[   12.206606] [<ffffffc000371740>] vfs_read+0x94/0x118
[   12.211564] [<ffffffc0003720f8>] SyS_read+0x64/0xb4
[   12.216436] [<ffffffc000203cb4>] el0_svc_naked+0x24/0x28

To avoid this, we should (a la https://lwn.net/Articles/628628/

) use the
wait_woken() function, which avoids the nested sleeping while still
handling races between waiting / wake-events.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: <Stable@vger.kernel.org> # 3.19+ for introduction of wake_woken
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

parent 522caebb

drivers/iio/industrialio-buffer.c

+17 −6

Original line number	Original line	Diff line number	Diff line
	@@ -107,6 +107,7 @@ ssize_t iio_buffer_read_first_n_outer(struct file filp, char __user buf,
	{		{
	struct iio_dev *indio_dev = filp->private_data;		struct iio_dev *indio_dev = filp->private_data;
	struct iio_buffer *rb = indio_dev->buffer;		struct iio_buffer *rb = indio_dev->buffer;
			DEFINE_WAIT_FUNC(wait, woken_wake_function);
	size_t datum_size;		size_t datum_size;
	size_t to_wait;		size_t to_wait;
	int ret;		int ret;
	@@ -131,19 +132,29 @@ ssize_t iio_buffer_read_first_n_outer(struct file filp, char __user buf,
	else		else
	to_wait = min_t(size_t, n / datum_size, rb->watermark);		to_wait = min_t(size_t, n / datum_size, rb->watermark);

			add_wait_queue(&rb->pollq, &wait);
	do {		do {
	ret = wait_event_interruptible(rb->pollq,		if (!indio_dev->info) {
	iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size));		ret = -ENODEV;
	if (ret)		break;
	return ret;		}

	if (!indio_dev->info)		if (!iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size)) {
	return -ENODEV;		if (signal_pending(current)) {
			ret = -ERESTARTSYS;
			break;
			}

			wait_woken(&wait, TASK_INTERRUPTIBLE,
			MAX_SCHEDULE_TIMEOUT);
			continue;
			}

	ret = rb->access->read_first_n(rb, n, buf);		ret = rb->access->read_first_n(rb, n, buf);
	if (ret == 0 && (filp->f_flags & O_NONBLOCK))		if (ret == 0 && (filp->f_flags & O_NONBLOCK))
	ret = -EAGAIN;		ret = -EAGAIN;
	} while (ret == 0);		} while (ret == 0);
			remove_wait_queue(&rb->pollq, &wait);

	return ret;		return ret;
	}		}