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 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
