2.2.15pre4 VM fix

[Theodore Y. Ts'o]

   Date:   Fri, 28 Jan 2000 19:48:27 +0300
   From: Ivan Kokshaysky <ink en jurassic.park.msu.ru>

   On Fri, Jan 28, 2000 at 02:40:30PM +0000, Alan Cox wrote:
   > > n_tty_open() has been caught with your patch.
   > > Thanks!
   > 
   > Do you know which drivers (serial,tty) you were using it. n_tty_open itself
   > seems ok, but the caller may be guilty

   It happened when ppp connection was terminated (remote end hangup).
   Serial driver is Comtrol Rocketport. The problem is repeatable
   (3 times last 20 hours), so I can investigate further to see who
   is the caller.

I think it's a flase positive.  It's happeninig because tty_do_hangup()
is calling ldisc.open --- which means n_tty_open() inside an interrupt
context.  n_tty_open() makes a check to see whether it is being called
inside an interrupt, and uses GFP_ATOMIC to avoid blocking inside the
interrupt.  


static int n_tty_open(struct tty_struct *tty)
{
	....
		get_zeroed_page(in_interrupt() ? GFP_ATOMIC : GFP_KERNEL);
	...
}

This should be OK, I think.

						- Ted

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