On 2011-01-18 14:26, Gilles Chanteperdrix wrote:
> Philippe Gerum wrote:
>> On Tue, 2011-01-18 at 10:54 +0100, Jan Kiszka wrote:
>>> On 2011-01-18 10:47, Jan Kiszka wrote:
>>>> On 2011-01-17 21:15, Jeff Weber wrote:
>>>>> 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"
>>>>>
>>>> A) In-kernel use of the Xenomai skins is deprecated, and mixing user and
>>>> kernel space use won't make it easier for you to overcome this in your
>>>> system.
>>>>
>>>> B) If you actually depend on a shared mutex (I would really recommend to
>>>> revalidate that need), you must create it in user space so that it gains
>>>> a user space compatible fastlock.
>>> Hmm, which just turned out to be impossible as rt_mutex_bind is only for
>>> user space.
>>>
>>> /me is now really unsure if we should fix it (beyond catching &
>>> reporting the invalid setup). Designing applications like this points
>>> out several potential technical and legal issues. Other opinions?
>>
>> No, I agree. The __in-kernel__ native API is almost dead (not the one
>> used from user-space obviously) and will be gone for Xenomai 3.x. We
>> don't need to pile up doomed code over dead code.
>>
>> But we really want to prevent such usage over 2.x, because it seems to
>> be leading to memory corruption. I can reproduce a similar issue here on
>> x86_64, which is silenced when moving the RT_MUTEX_INFO buffer, and I
>> don't think rt_mutex_inquire() has any memory overwrite issue.
>
> If I agree that the in-kernel native API is deprecated. If we look at
> it, we see that the rt_mutex_create implementation was made much more
> complicated than, for instance, the one of the posix skin one which
> allows Jeff's case to work correctly. I have to admit that I am puzzled
> as to why such complication.
I heavily doubt it will work. The mutex init paths the POSIX skin takes
for in-kernel objects are as different from user space as they are for
Native.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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