Hi Lars, 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: > [...] > > Have any of you seen this kind of issue before (perhaps most IIO users > > are not using CONFIG_DEBUG_ATOMIC_SLEEP)? If the WARNING is really > > correct, then this problem has really been around a while. It looks like > > we have a wait_event_interruptible() called, with this call chain in the > > 'condition' path: > > > > iio_buffer_ready() > > -> iio_buffer_data_available() (i.e., iio_kfifo_buf_data_available()) > > -> mutex_lock() > > > > Calling mutex_lock() means we clobber the TASK_INTERRUPTIBLE state with > > TASK_RUNNING -- hence, the WARNING. Should this be using a spinlock > > instead? Or is there some way to refactor this to avoid calling these > > sleeping functions in the wait_event*() condition? > > Hi, > > 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/).
Ah, thanks for the pointer. I thought this problem seemed familiar, but I couldn't find a canonical solution. The wait_woken() solution looks like a good starting point, although it's definitely got more boilerplate... It also requires a 'timeout'; I guess we'd want MAX_SCHEDULE_TIMEOUT for this case? Do you want to cook a patch, or should I? Brian
