[uml-devel] Problem with pthread applications in UML

[Shane K. <sh...@ti...>]

Jeff & Co.,

I saw a report of threading problems on the user list, but I'm not
currently on that list.  And this doesn't seem too related.  Anyway...

I just downloaded and compiled a kernel with uml-patch-2.4.17-9.bz2, and
booted up the Red Hat 7.2 image.  It consumed 100% of the CPU all of the
time.  I shut down various services, and eventually got it to run idle.

The problem turned out to be that any program running pthreads spins.
Here's a short sample:

*** begin foo.c ***
#include <pthread.h>
#include <stdio.h>

void *
thread (void *dummy)
{
    for (;;) {
        sleep(60);
    }
}

int 
main ()
{
    pthread_t tid;

    if (pthread_create(&tid, NULL, thread, NULL) != 0) {
        fprintf(stderr, "Error %d creating thread\n");
        return 1;
    }
    pthread_join(tid, NULL);
    return 0;
}
*** end foo.c **

Run with:

$ gcc -o foo foo.c -lpthread
$ ./foo

UML has two threads, one using 2/3 of the CPU, the other the remaining
1/3.  Additionally, the threads appear to ignore any signal but SIGKILL,
although the parent process gets a return from wait().

Needless to say, this program consumes no CPU when run under the host
kernel.  ;)

-- 
Shane
Carpe Diem