[BUG][2.4] /proc/kcore is a random generator ?

[Willy Tarreau <willy@w.ods.org>]

Hi all,

I'm encountering a rather strange behaviour here with 2.4.25 on a P4 HT,
even when I boot it with "nosmp" :
  - du /proc/kcore says '525255' (I have 512 MB RAM)
  - if I do it again many several times, sometimes it says '0'
  - after a moment (or several tests, I don't know), it stabilizes to some
    value (either 0 or 525255).
  - then, just starting vmstat, or logging into the system is enough to
    make it switch to the other value.

At first, I had the feeling that it displayed '0' when I have an even number
of processes, and 525255 when I have an odd number, but it's not even the case.
Once it doesn't move by itself, a few fork/exec are enough to switch the value.

If I boot in HT mode, sometimes I can reliably make it display 0 and 525255
alternatively, just as if the pid parity or CPU number was involved in the
result.

Update: same results with 2.4.26-pre1. du from coreutils 4.5.4 and 5.0.

This is amazing. Did anyone notice this ? A friend just told me that plain
2.4.22 on his notebook does the same !

Regards,
Willy