Messages in this thread | | | Subject | Re: __might_sleep in uio_read()? | From | Andy Grover <> | Date | Thu, 3 Sep 2015 13:12:28 -0700 |
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On 09/03/2015 12:12 PM, Greg KH wrote: > 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?
I'm working on drivers/target/target_core_user.c, a SCSI userspace passthrough that was added in 3.18, aka TCMU, which uses uio.
The checks for !TASK_RUNNING were added in 3.19 (8eb23b9f3 and 00845eb96)
...and I'm just getting back to TCMU development after a bit, so maybe I'm the first one to call uio_read since those checks were added in 3.19?
-- Andy
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