From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4D359732.8050504@domain.hid> Date: Tue, 18 Jan 2011 14:35:46 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <4D3561A5.6000804@domain.hid> <4D35635A.4040403@domain.hid> <1295347610.1857.74.camel@domain.hid> <4D359506.6090907@domain.hid> In-Reply-To: <4D359506.6090907@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] segfault sharing mutex from kernel space to user space List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: "xenomai@xenomai.org" 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 >>>>> #include >>>>> #include >>>>> #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 >>>>> #include >>>>> #include >>>>> #include >>>>> >>>>> #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@domain.hid%", '\000' >>>>> , >>>>> 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