Here is the race: CPU #0 CPU#1
cleanup_mnt nfs41_callback_svc (get xprt from the list) nfs_callback_down ... ... ... svc_close_net ... ... ... svc_xprt_free ... svc_bc_sock_free bc_svc_process kfree(xprt) svc_process_common rqstp->rq_xprt->xpt_ops (use after free) The problem is that per-net SUNRPC transports shutdown is done regardless current callback execution. This is a race leading to transport use-after-free in callback handler. This patch fixes it in stright-forward way. I.e. it protects callback execution with the same mutex used for per-net data creation and destruction. Hopefully, it won't slow down NFS client significantly. https://jira.sw.ru/browse/PSBM-75751 v2: Fix mutex deadlock, when shutdown callback waits for thread to exit (with mutex taken), while thread wait for the mutex to take. Signed-off-by: Stanislav Kinsburskiy <skinsbur...@virtuozzo.com> --- fs/nfs/callback.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c index 0beb275..eed861a 100644 --- a/fs/nfs/callback.c +++ b/fs/nfs/callback.c @@ -118,6 +118,11 @@ nfs41_callback_svc(void *vrqstp) continue; prepare_to_wait(&serv->sv_cb_waitq, &wq, TASK_INTERRUPTIBLE); + + if (!mutex_trylock(&nfs_callback_mutex) && + kthread_should_stop()) + return 0; + spin_lock_bh(&serv->sv_cb_lock); if (!list_empty(&serv->sv_cb_list)) { req = list_first_entry(&serv->sv_cb_list, @@ -129,8 +134,10 @@ nfs41_callback_svc(void *vrqstp) error = bc_svc_process(serv, req, rqstp); dprintk("bc_svc_process() returned w/ error code= %d\n", error); + mutex_unlock(&nfs_callback_mutex); } else { spin_unlock_bh(&serv->sv_cb_lock); + mutex_unlock(&nfs_callback_mutex); schedule(); finish_wait(&serv->sv_cb_waitq, &wq); } _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel