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Date: Thu, 3 Sep 2015 14:26:16 +0200 From: Michal Hocko <mhocko@...nel.org> To: Andy Grover <agrover@...hat.com> Cc: hjk@...sjkoch.de, Greg KH <gregkh@...uxfoundation.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: __might_sleep in uio_read()? 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 { -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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