Re: Sleeping thread not receive signal until it wakes up

["Luong Ngo" <luong.ngo@gmail.com>]

Hi Dick,
Thanks for your response. In my ioctl in the kernel, I use
interruptible_sleep_on to sleep on a queue and will be wake up by the
the ISR routine when interrupt happens, so  isn't
interruptible_sleep_on supposed to be interruptable, from its name? I
am using kernel 2.6.14.

Thanks again,
LNgo

On 3/7/07, linux-os (Dick Johnson) <linux-os@analogic.com> wrote:
>
> On Wed, 7 Mar 2007, Luong Ngo wrote:
>
> > Hi all,
> >
> > I am having this problem. I have a process with 2 threads created. One
> > of the thread will keep calling IOCTL  to get information from the
> > kernel and will be blocked if there is no new information. If there is
> > information retured, the thread will be checked to see if any error
> > happens and trigger an action. Since we have no way to know if the
> > error is gone (Hardware provides no signal), so what we do is when
> > trigger an action for the error, we will set an timer using alarm()
> > and register a SIGALRM handler in the thread by using sigaction. After
> > setting the alarm, the thread will loop back and call IOCTL, which
> > could cause it to be put to sleep. The problem is the SIGALRM handler
> > does not receive the SIGALRM while the thread is being blocked by
> > IOCTL. And if we generated some event so that the IOCTL is returned
> > with new information, the SIGALRM handler is invoked right away.
> > However, as I read the manual, which says a thread/process should be
> > waken up even when it sleeps if there is a signal delivered to it. Am
> > I right?
> > One thing I don't know it mattters or not is that I am not using
> > sigwait to block the process and wait for signal because the thread
> > need to go back to the IOCTL call and be slept on that. So I used
> > sigaction to register the signal handler in hope that this handler wil
> > be invoked by the kernel when there is an SIGALRM delivered to the
> > thread.
> > Could anyone tell me if I did something wrong and what is the correct
> > way to achieve this task? I tried to avoid creating another thread
> > which will call sigwait and block until the IOCTL thread send it
> > explicitly a signal because I want to use timer.
> >
> >
> > Thank you in advance,
> > LNgo
> > -
>
> Later versions of the kernel lock the kernel when an ioctl() is
> entered. This means that if you sleep in the ioctl(), nothing
> will get scheduled.
>
> You can do the following (possibly unsafe) in your ioctl():
>
>     int locked = kernel_locked();
>
>     ......... code
>     ......... code
>
>     if(locked)  // Before sleeping section
>        unlock_kernel();
>     .......... sleeping code
>     if(locked)  // After sleeping section
>         lock_kernel();
>
>
>
> Cheers,
> Dick Johnson
> Penguin : Linux version 2.6.16.24 on an i686 machine (5592.71 BogoMips).
> New book: http://www.AbominableFirebug.com/
> _
> \x1a\x04
>
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>