[Xenomai-help] segfault sharing mutex from kernel space to user space

[Jeff Weber]

I get a segfault when attempting to rt_mutex_acquire a mutex created in
kernel space.  I've reduced the issue to the following sample code.
Help finding my mistake is appreciated.

TIA,
Jeff


Kernel space Code:
#include <linux/module.h>
#include <linux/init.h>
#include <native/mutex.h>
#include "testAPI.h"  /* defines MTXNAME */

#define MODNAME  "XenoTest"

static RT_MUTEX sMtx;

static int __init mymodule_init(void)
{
    int status;

    status = rt_mutex_create(&sMtx, MTXNAME);
    if (status) {
    printk ("rt_mutex_create: %d\n", status);
        return 1;
    }

    printk ("loaded module %s\n", MODNAME);
    return 0;
}

static void __exit mymodule_exit(void)
{
    rt_mutex_delete(&sMtx);

    printk ("unloaded module %s\n", MODNAME);
    return;
}

module_init(mymodule_init);
module_exit(mymodule_exit);

MODULE_LICENSE("GPL");



User space Code:
#include <stdio.h>
#include <sys/mman.h>
#include <native/mutex.h>
#include <native/task.h>

#include "testAPI.h"    /* defines MTXNAME */

#define PRIO    0
#define MODE    0

int main(void)
{
    RT_MUTEX mtx;
    RT_TASK  tsk;
    RT_MUTEX_INFO info;
    int status;

    mlockall(MCL_CURRENT|MCL_FUTURE);

    status = rt_task_shadow(&tsk, NULL, PRIO, MODE);
    if (status) {
        fprintf(stderr, "rt_task_shadow: %d\n", status);
        return 1;
    }

    status = rt_mutex_bind(&mtx, MTXNAME, TM_INFINITE);
    if (status) {
        fprintf(stderr, "rt_mutex_bind: %d\n", status);
        return 1;
    }

    status = rt_mutex_inquire(&mtx, &info);
    if (status) {
        fprintf(stderr, "rt_mutex_inquire: %d\n", status);
        return 1;
    }

    status = rt_mutex_acquire(&mtx, TM_INFINITE); /* SEGFAULT HERE! */
    if (status) {
        fprintf(stderr, "rt_mutex_acquire: %d\n", status);
        return 1;
    }

    status = rt_mutex_release(&mtx);
    if (status) {
        fprintf(stderr, "rt_mutex_release: %d\n", status);
        return 1;
    }

    printf("test success\n");   // back to primary mode
    return 0;
}

my kernel

backtrace:
Program terminated with signal 11, Segmentation fault.
#0  0xb770077a in xnarch_atomic_cmpxchg (v=0xb777ac00, old=0, newval=21)
    at ../../../src/include/asm/xenomai/atomic.h:95
95              __asm__ __volatile__(LOCK_PREFIX "cmpxchgl %1,%2"
(gdb) bt full
#0  0xb770077a in xnarch_atomic_cmpxchg (v=0xb777ac00, old=0, newval=21)
    at ../../../src/include/asm/xenomai/atomic.h:95
        ptr = 0xb777ac00
        prev = 4294967295
#1  0xb7700815 in xnsynch_fast_acquire (fastlock=0xb777ac00, new_ownerh=21)
    at ../../../include/nucleus/synch.h:52
        lock_state = 3077595124
#2  0xb7700c3a in rt_mutex_acquire_inner (mutex=0xbfecd690, timeout=0,
    mode=XN_RELATIVE) at mutex.c:83
        err = 134513420
        cur = 21
#3  0xb7700e01 in rt_mutex_acquire (mutex=0xbfecd690, timeout=0) at
mutex.c:129
No locals.
#4  0x0804884a in main () at uspace.c:38
        mtx = {opaque = 19, fastlock = 0xb777ac00, lockcnt = 0}
        tsk = {opaque = 21, opaque2 = 3075921616}
        info = {locked = 0, nwaiters = 0,
          name = "TestMtx\000\000\000\060\000@\236i\340\000\177%", '\000'
<repeats 12 times>,
          owner =
"\000\000\000\000\364\036\331\336\020\037\331\336\365Pd\340\005\005UU\000\037\331\336\000\000\000\000\023\000\000"}
        status = 0

my config:
arch: x86
linux: 2.6.35.10
xenomai: 2.5.5.2

BTW: I did a checkout of git tag v2.5.5.2, and XENO_VERSION_STRING is
"2.5.5.1"

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