[uml-devel] uml hangs in skas mode

[Gerd Knorr <kraxel@bytesex.org>]

  Hi,

I ran into a uml kernel issue with the suse hardware detection tool
(hwinfo).  hwinfo tries to detect whenever it runs within vmware or
not, and this doesn't work.  hwinfo just hangs forever.  The relevant
part of the code to reproduce it is below.

What I've figured so far:

  * hwinfo blocks in the waitpid() call, waiting for the forked
    child finish.
  * It happens in skas mode only, tt mode is fine.
  * It happens on a completely idle machine only.  As soon as I start to
    do something in another shell hwinfo continues to run (=> scheduler
    race?) 
  * It doesn't happen if I try to "strace -f" the process.

Any idea?

  Gerd

==============================[ cut here ]==============================
#define _GNU_SOURCE		/* we want memmem() */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>

#include <sys/types.h>
#include <sys/wait.h>

void sigsegv_handler(int signum) { exit(77); }

int chk_vmware(void)
{
  static int is_vmware = -1;
  int child, status;

  /* do the check only once */
  if(is_vmware < 0) {

    child = fork();

    if(child == 0) {
      signal(SIGSEGV, sigsegv_handler);

      asm(
        "push %ebx\n"
        "\tpush %edx\n"
        "\tpush %eax\n"
        "\tpush %ecx\n"
        "\tmov $0x564d5868,%eax\n"
        "\tmov $0xa,%ecx\n"
        "\tmov $0x5658,%edx\n"
        "\tin (%dx),%eax\n"
        "\tpop %ecx\n"
        "\tpop %eax\n"
        "\tpop %edx\n"
        "\tpop %ebx\n"
      );

      _exit(66);
    }
    else {
      if(waitpid(child, &status, 0) == child) {
        status = WEXITSTATUS(status);
        if(status == 66) is_vmware = 1;
        if(status == 77) is_vmware = 0;
      }
    }
  }
  return is_vmware;
}

int main(int argc, char *argv[])
{
	int rc;

	fprintf(stderr, "check for vmware... ");
	rc = chk_vmware();
	fprintf(stderr, "%s\n", rc ? "yes" : "no");
	return rc;
}


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