[BUG] 2.[45] ioperm fix seems broken (was Re: Linux 2.4.21-rc3)

[Barry K. Nathan]

On Fri, May 23, 2003 at 07:32:49AM +0200, Marc-Christian Petersen wrote:
> nono, this fix is the right one. All works fine :-)

Nope, the ioperm fix seems to be breaking something alright. Eventually
I was able to reproduce this on 2.5.69-mm[78] as well.

Here's my distilled test case. (My real test case is FCE Ultra, compiled
for svgalib. The crash happens in svgalib, version 1.4.3-cl1 if that
matters.)

---cut here---
#include <sys/io.h>

int main()
{
        char c;

        if (ioperm(0x3b4, 0x3df - 0x3b4 + 1, 1)) {
                perror("ugh");
                exit(1);
        } else printf("ioperm succeeded\n");

        printf("About to perform inb...\n");
        c = inb(0x3cc);
        printf("result: %d\n", (int)c);
        return 0;
}
---cut here---

Steps to reproduce:

1. Compile this program (e.g., "gcc iopt.c" or "gcc -O2 iopt.c").
2. Switch to a text virtual console.
3. Log in as root (or log in as a normal user and su to root). This
program does not crash from within X, nor does it crash from an SSH
session.
4. Run the program (e.g., "./a.out").
5. The program will probably crash after "About to perfrom inb" but
before "result:...". If not, try it again a few times. If it still
doesn't crash for you, try logging in on another virtual console, or
just wait a few minutes and try again. Sometimes it's 10% reproducible
and sometimes it's well over 90% reproducible...
6. Examine the code/core using gdb. Notice that the inb caused the
segfault.

The real-world effect of this bug is that my NES emulator just broke
almost completely. :( Interestingly, a somewhat reliable workaround for
fceu (but not for my test case AFAICT) is to strace it rather than
running it directly -- then it usually doesn't segfault.

-Barry K. Nathan <[e-mail]>