[PATCH 4.4 065/113] iio: fix sched WARNING "do not call blocking ops when !TASK_RUNNING"

Greg Kroah-Hartman
2016-09-05T16:53:24Z

From: Brian Norris <briannorris@chromium.org>

commit fcf68f3c0bb2a541aa47a2a38b8939edf84fd529 upstream.

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>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/iio/industrialio-buffer.c | 25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)

--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -107,6 +107,7 @@ ssize_t iio_buffer_read_first_n_outer(st
{
struct iio_dev *indio_dev = filp->private_data;
struct iio_buffer *rb = indio_dev->buffer;
+ DEFINE_WAIT_FUNC(wait, woken_wake_function);
size_t datum_size;
size_t to_wait;
int ret;
@@ -131,19 +132,29 @@ ssize_t iio_buffer_read_first_n_outer(st
else
to_wait = min_t(size_t, n / datum_size, rb->watermark);

+ add_wait_queue(&rb->pollq, &wait);
do {
- ret = wait_event_interruptible(rb->pollq,
- iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size));
- if (ret)
- return ret;
-
- if (!indio_dev->info)
- return -ENODEV;
+ if (!indio_dev->info) {
+ ret = -ENODEV;
+ break;
+ }
+
+ if (!iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size)) {
+ 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);
if (ret == 0 && (filp->f_flags & O_NONBLOCK))
ret = -EAGAIN;
} while (ret == 0);
+ remove_wait_queue(&rb->pollq, &wait);

return ret;
}