在 2024/11/26 1:32, Mark Liam Brown 写道:
On Mon, Nov 25, 2024 at 1:48 PM Li Lingfeng <lilingfeng3@xxxxxxxxxx> wrote:Hi, we have found a hungtask issue recently. Commit 7746b32f467b ("NFSD: add shrinker to reap courtesy clients on low memory condition") adds a shrinker to NFSD, which causes NFSD to try to obtain shrinker_rwsem when starting and stopping services. Deploying both NFS client and server on the same machine may lead to the following issue, since they will share the global shrinker_rwsem. nfsd nfs drop_cache // hold shrinker_rwsem write back, wait for rpc_task to exit // stop nfsd threads svc_set_num_threads // clean up xprts svc_xprt_destroy_all rpc_check_timeout rpc_check_connected // wait for the connection to be disconnected unregister_shrinker // wait for shrinker_rwsem Normally, the client's rpc_task will exit after the server's nfsd thread has processed the request. When all the server's nfsd threads exit, the client’s rpc_task is expected to detect the network connection being disconnected and exit. However, although the server has executed svc_xprt_destroy_all before waiting for shrinker_rwsem, the network connection is not actually disconnected. Instead, the operation to close the socket is simply added to the task_works queue. svc_xprt_destroy_all ... svc_sock_free sockfd_put fput_many init_task_work // ____fput task_work_add // add to task->task_works The actual disconnection of the network connection will only occur after the current process finishes. do_exit exit_task_work task_work_run ... ____fput // close sock Although it is not a common practice to deploy NFS client and server on the same machine, I think this issue still needs to be addressed, otherwise it will cause all processes trying to acquire the shrinker_rwsem to hang.I disagree with that comment. Most small companies have NFS client and NFS server on the same machine, the client being used to allow logins by users, or to support schroot or containers. Mark
Sorry for my hasty conclusion. By the way, nfsd_reply_cache_shrinker triggers this too. Li
