[SPDK] 答复: Re: thread->msg_cache is not safe when multiple threads send messages to same spdk_th read

Dear maintainer Jim, thank you for your reply.

After reading your email, I know I have used the wrong way to submiting io.

When I create a thread to submit io, I don't create spdk_thread structure for the thread, this structure only be created in spdk_reactors_start api for every lcore;
Must I create spdk_thread structure for every submit thread?


Please give me some advice, thank you!


-----邮件原件-----
发件人: Harris, James R [mailto:james.r.harris(a)intel.com] 
发送时间: 2020年9月16日 3:32
收件人: Storage Performance Development Kit <spdk(a)lists.01.org>
主题: [SPDK] Re: thread->msg_cache is not safe when multiple threads send messages to same spdk_thread

Hi,

local_thread gets its value from _get_thread().  _get_thread() returns the thread-local spdk_thread structure for the calling thread. So if multiple threads call spdk_thread_send_msg() in parallel, they will each use their own thread-local spdk_thread structure and no lock or synchronization is needed.

-Jim

On 9/15/20, 6:33 AM, "sunshihao(a)huawei.com" <sunshihao(a)huawei.com> wrote:

    hello，maintainer：
    when i use spdk api spdk_thread_send_msg to send io read/write msg，i found a bug：
    multiple threads send msg to one spdk_thread，they may get msg form local_thread->msg_cache，there is not a lock or cas to 
    ensure the safety of the linked list。 

             msg = NULL;

    	if (local_thread != NULL) {
    		if (local_thread->msg_cache_count > 0) {
    				msg = SLIST_FIRST(&local_thread->msg_cache);    /* here maybe not thread safe */
    				assert(msg != NULL);
    				SLIST_REMOVE_HEAD(&local_thread->msg_cache, link);
    				local_thread->msg_cache_count--;
    		}
    	}

    i don't konw whether is my wrong way to use spdk_thread_send_msg  or the list is not safe，so please give me some advice。
    Thank you！
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