O_NONBLOCK setting "leak" outside of a process??

[Denis Vlasenko <vda.linux@googlemail.com>]

Hi,

I am currently on Linux 2.6.18, x86_64.
I came across strange behavior while working on one
of busybox applets. I narrowed it down to these two
trivial testcases:

#include <unistd.h>
#include <fcntl.h>
int main() {
        fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) | O_NONBLOCK);
        return 0;
}

#include <unistd.h>
#include <fcntl.h>
int main() {
        fcntl(0, F_SETFL, fcntl(0, F_GETFL, 0) & ~O_NONBLOCK);
        return 0;
}

If I run "nonblock" in Midnight Commander in KDE's Konsole,
screen redraw starts to work ~5 times slower. For example,
Ctrl-O ("show/hide panels" in MC) takes ~0.5 sec to redraw.
This persists after the program exist (which it
does immediately as you see).
Running "block" reverts things to normal.

I mean: how can O_NONBLOCK _issued in a process which
already exited_ have any effect whatsoever on MC or Konsole?
They can't even know that it did it, right?

Either I do not know something subtle about Unix or some sort
of bug is at work.

Any advice?
--
vda