Date: Wed, 4 May 2005 11:43:18 -0700
From: Chris Wedgwood <cw@f00f.org>
To: Andr? Pereira de Almeida <andre@cachola.com.br>
Cc: linux-kernel@vger.kernel.org
Subject: Re: A patch for the file kernel/fork.c
Message-ID: <20050504184318.GA644@taniwha.stupidest.org>
References: <4278E03A.1000605@cachola.com.br> <20050504175457.GA31789@taniwha.stupidest.org> <427913E4.3070908@cachola.com.br>
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On Wed, May 04, 2005 at 03:26:44PM -0300, Andr? Pereira de Almeida wrote:

> >>-       if (tsk->clear_child_tid && atomic_read(&mm->mm_users) > 1) {
> >>+       if (mm && tsk->clear_child_tid && atomic_read(&mm->mm_users) > 1)

> In a preemptible kernel with the serport module and a serial port try to
> run the following program:
>
> int main(int argc, char **argv)
> {
>        int ldisc,fd;
>
>        fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NONBLOCK);
>        ldisc = N_MOUSE;
>        ioctl(fd, TIOCSETD, &ldisc);
>        read(fd, NULL, 0);
>        return 0;
> }
>
> and kill it.  In my case it will hang the computer. I think this is
> a problem with the serport module. With this patch, the serial mouse
> stop working, but the computer don't hang.

then above something like:

     BUG_ON(!mm);

or something might be better and eyeball the stack trace.

-
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