Messages in this thread | | | Subject | Questions about the SYSVIPC share memory on NOMMU uClinux architecture | From | "Wu, Bryan" <> | Date | Fri, 02 Mar 2007 18:33:49 +0800 |
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Hi folks,
Recently, I was struggling in a bug about the shm->nattch. Actually, the test case is from LTP kernel/syscall/ipc/shmctl/shmctl01.c code. We ported it to the uClinux-blackfin platform.
The algorithm is very simple. a) the parent process will create a share memory b) parent will vfork/execlp 4 children process c) children will call shmat() attach to the share memory (shm->nattch should be increased), then children will pause() d) parent call shmclt() to get the share memory nattch, if nattch != 4, then the testcase will fail.
In our uClinux-blackfin platform, nattch = 1.
So I dig into the source code ipc/shm.c, then there are some questions about the code.
a) in function do_shmat(), after nattch++ why nattch-- as following: ================================================================================ user_addr = (void*) do_mmap (file, addr, size, prot, flags, 0);
// here no return or goto valid place.
invalid: up_write(¤t->mm->mmap_sem);
mutex_lock(&shm_ids(ns).mutex); shp = shm_lock(ns, shmid); BUG_ON(!shp); shp->shm_nattch--; /* Why??? */ if(shp->shm_nattch == 0 && shp->shm_perm.mode & SHM_DEST) shm_destroy(ns, shp); else shm_unlock(shp); mutex_unlock(&shm_ids(ns).mutex);
*raddr = (unsigned long) user_addr; err = 0; if (IS_ERR(user_addr)) err = PTR_ERR(user_addr); out: return err; ================================================================================
b) do_mmap() -> mm/nommu.c do_mmap_pgoff() When create a new vma structure, shm_open(), shm_inc() will be called. Then nattch++. So the nattch counting is disordered.
Please give me some hint about it. Actually, this case can pass on X86 platform
Thanks -Bryan Wu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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