c – mmap / munmap问题 – 在783rd迭代后得到总线错误？

2019年7月29日 242次阅读

好的,这是设置：我在HPC工作,我们正在准备扩展到数万个节点的需求.为了解决这个问题,我实现了一个本地进程,用于缓存每个节点上的信息,以减少网络流量.然后它通过共享内存公开此信息.基本逻辑是有一个众所周知的共享内存块,它包含当前缓存表的名称.发生更新时,缓存工具会创建一个新的共享内存表,填充它,然后使用新表的名称更新已知块.

代码似乎是工作查找(例如,valgrind说没有内存泄漏),但是当我故意对其进行压力测试时,前783个更新工作完全正常 – 但是在784号,当我尝试写入时,我收到了SIGBUS错误映射内存.

如果问题是打开文件太多(因为我正在泄漏文件描述符),我希望shm_open()失败.如果问题是我正在泄漏映射内存,我希望mmap()失败或valgrind报告泄漏.

这是代码片段.任何人都可以提出建议吗？

int
initialize_paths(writer_t *w, unsigned max_paths)
{
int err = 0;
reader_t *r = &(w->unpublished);

close_table(r,PATH_TABLE);

w->max_paths = max_paths;

err = open_table(r, PATH_TABLE, O_RDWR | O_CREAT, max_paths, 0);

return err;
}

static void
close_table(reader_t *r, int table)
{
    if (r->path_table && r->path_table != MAP_FAILED) {
       munmap(r->path_table,r->path_table->size);
       r->path_table=NULL;
    }
    if (r->path_fd>0) { close(r->path_fd); r->path_fd=0; }
}


static int
open_table(op_ppath_reader_t *r, int table, int rw, unsigned c, unsigned c2)
{
// Code omitted for clarity
if (rw & O_CREAT) {
    prot = PROT_READ | PROT_WRITE;
} else {
    // Note that this overrides the sizes set above.
    // We will get the real sizes from the header.
    prot = PROT_READ;
    size1 = sizeof(op_ppath_header_t);
    size2 = 0;
}

fd = shm_open(name, rw, 0644);
if (fd < 0) {
    _DBG_ERROR("Failed to open %s\n",name);
    goto error;
}

if (rw & O_CREAT) {
    /* Create the file at the specified size. */
    if (ftruncate(fd, size1 + size2)) {
        _DBG_ERROR("Unable to size %s\n",name);
        goto error;
    }
}

h = (op_ppath_header_t*)mmap(0, size1 + size2, prot, MAP_SHARED, fd, 0);
if (h == MAP_FAILED) {
    _DBG_ERROR("Unable to map %s\n",name);
    goto error;
}

if (rw & O_CREAT) {
    /*
     * clear the table & set the maximum lengths.
     */
    memset((char*)h,0,size1+size2);  -- SIGBUS OCCURS HERE
    h->s1 = size1;
    h->s2 = size2;
} else {
// more code omitted for clarity.
}

更新：

以下是故障的一些示例调试输出：

NOTICE: Pass 783: Inserting records.
NOTICE: Creating the path table.
TRC: initialize_paths[
TRC: close_table[
TRC: close_table]
TRC: open_table[
DBG: h=0x0x2a956b2000, size1=2621536, size2=0

这是前一次迭代的相同输出：

NOTICE: Pass 782: Inserting records.
NOTICE: Creating the path table.
TRC: initialize_paths[
TRC: close_table[
TRC: close_table]
TRC: open_ppath_table[
DBG: h=0x0x2a956b2000, size1=2621536, size2=0
TRC: open_ppath_table]
TRC: op_ppath_initialize_paths]

请注意,指针地址有效,大小也是如此.

GDB以这种方式报告崩溃：

Program received signal SIGBUS, Bus error.
[Switching to Thread 182895447776 (LWP 5328)]
0x00000034a9371d20 in memset () from /lib64/tls/libc.so.6
(gdb) where
#0  0x00000034a9371d20 in memset () from /lib64/tls/libc.so.6
#1  0x0000002a955949d0 in open_table (r=0x7fbffff188, table=1, rw=66,
c=32768, c2=0) at ofedplus_path_private.c:294
#2  0x0000002a95595280 in initialize_paths (w=0x7fbffff130,
    max_paths=32768) at path_private.c:567
#3  0x0000000000402050 in server (fname=0x7fbffff270 "gidtable", n=10000)
    at opp_cache_test.c:202
#4  0x0000000000403086 in main (argc=6, argv=0x7fbffff568)
    at opp_cache_test.c:542

(GDB)

当在以下行上设置h-> size1时,删除memset仍会导致SIGBUS – 而size1是映射区域的前4个字节.

最佳答案 SIGBUS可能是由对SHM对象的许多引用引起的.

查看上面的代码,使用shm_open(),mmap(),munmap()但是

你错过了shm_unlink().

由于* shm_open / shm_close的联机帮助页指出这些对象是引用计数.

The operation of shm_unlink is analogous to unlink(2): it removes a shared memory object
name, and, once all processes have unmapped the object, deallocates and destroys the
contents of the associated memory region.
After a successful shm_unlink, attempts to shm_open an object with the same
name will fail (unless O_CREAT was specified, in which case a new, distinct object is created).

也许这些信息有助于解决您的问题.

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