[PATCH] iio: fix sched WARNING "do not call blocking ops when !TASK_RUNNING"
From: Brian Norris
Date: Thu Aug 04 2016 - 04:26:37 EST
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@xxxxxxxxxxxx>
---
On Tue, Aug 02, 2016 at 07:04:07PM +0200, Lars-Peter Clausen wrote:
> On 08/02/2016 06:57 PM, Brian Norris wrote:
> > On Tue, Aug 02, 2016 at 03:06:39PM +0200, Lars-Peter Clausen wrote:
> >> On 08/02/2016 03:12 AM, Brian Norris wrote:
> >>> I'm seeing the following warnings when I read from an IIO char device,
> >>> with CONFIG_DEBUG_ATOMIC_SLEEP=y. I'm testing a v4.4 kernel, but AFAICT,
> >>> nothing too relevant has changed between that and v4.7:
[...]
> >> Yes, this is an issue, thanks for pointing this out. It has been there for a
> >> while, my fault, sorry for that. We need a solution like pointed out in this
> >> article (https://lwn.net/Articles/628628/).
[...]
> > Do you want to cook a patch, or should I?
>
> Go ahead.
Done!
Tested on v4.4.
drivers/iio/industrialio-buffer.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 90462fcf5436..2ad10e0190d8 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -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_buffer *rb = indio_dev->buffer;
+ DEFINE_WAIT_FUNC(wait, woken_wake_function);
size_t datum_size;
size_t to_wait;
int ret;
@@ -132,10 +133,13 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
to_wait = min_t(size_t, n / datum_size, rb->watermark);
do {
- ret = wait_event_interruptible(rb->pollq,
- iio_buffer_ready(indio_dev, rb, to_wait, n / datum_size));
- if (ret)
- return ret;
+ add_wait_queue(&rb->pollq, &wait);
+ while (!iio_buffer_ready(indio_dev, rb, to_wait,
+ n / datum_size)) {
+ wait_woken(&wait, TASK_INTERRUPTIBLE,
+ MAX_SCHEDULE_TIMEOUT);
+ }
+ remove_wait_queue(&rb->pollq, &wait);
if (!indio_dev->info)
return -ENODEV;
--
2.8.1.340