Messages in this thread | | | Date | Thu, 3 Sep 2015 12:12:39 -0700 | From | Greg KH <> | Subject | Re: __might_sleep in uio_read()? |
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On Thu, Sep 03, 2015 at 11:47:34AM -0700, Andy Grover wrote: > On 09/03/2015 05:26 AM, Michal Hocko wrote: > >On Wed 02-09-15 15:45:10, Andy Grover wrote: > >>Hi Hans and Greg, > >> > >>Is this an issue with uio? I swear it didn't used to throw this warning... > >> > >>Thanks -- Andy > >> > >>[ 5174.883261] ------------[ cut here ]------------ > >>[ 5174.883617] WARNING: CPU: 0 PID: 1532 at > >>/home/agrover/git/kernel/kernel/sched/core.c:7389 __might_sleep+0x7d/0x90() > >>[ 5174.884407] do not call blocking ops when !TASK_RUNNING; state=1 set at > >>[<ffffffffa02a5821>] uio_read+0x91/0x170 [uio] > > > >The warning says that the driver is calling copy_to_user with > >TASK_INTERRUPTIBLE which is wrong in general because this context can > >sleep and a schedule would destroy the state. It doesn't matter here > >because the code would break out from the loop regardless of the > >copy_to_user return value. > > > >I assume that TASK_INTERRUPTIBLE is necessary before the event_count > >check to prevent from wake up races. If that is the case then you can > >simply do: > >diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c > >index 3257d4220d01..7d8959e3833b 100644 > >--- a/drivers/uio/uio.c > >+++ b/drivers/uio/uio.c > >@@ -524,6 +524,7 @@ static ssize_t uio_read(struct file *filep, char __user *buf, > > > > event_count = atomic_read(&idev->event); > > if (event_count != listener->event_count) { > >+ __set_current_state(TASK_RUNNING); > > if (copy_to_user(buf, &event_count, count)) > > retval = -EFAULT; > > else { > > > > This certainly makes the warning go away. If this looks good to everyone > else can we get this change in?
What changed to require this? Why is this suddenly showing up now?
thanks,
greg k-h
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