From patchwork Fri Apr 10 11:47:20 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: He Zhe X-Patchwork-Id: 11483191 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A54D814B4 for ; Fri, 10 Apr 2020 11:47:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F82C215A4 for ; Fri, 10 Apr 2020 11:47:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726179AbgDJLra (ORCPT ); Fri, 10 Apr 2020 07:47:30 -0400 Received: from mail1.windriver.com ([147.11.146.13]:62512 "EHLO mail1.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725930AbgDJLra (ORCPT ); Fri, 10 Apr 2020 07:47:30 -0400 Received: from ALA-HCA.corp.ad.wrs.com (ala-hca.corp.ad.wrs.com [147.11.189.40]) by mail1.windriver.com (8.15.2/8.15.2) with ESMTPS id 03ABlNfQ000030 (version=TLSv1 cipher=AES256-SHA bits=256 verify=FAIL); Fri, 10 Apr 2020 04:47:23 -0700 (PDT) Received: from pek-lpg-core3.wrs.com (128.224.153.232) by ALA-HCA.corp.ad.wrs.com (147.11.189.40) with Microsoft SMTP Server id 14.3.487.0; Fri, 10 Apr 2020 04:47:22 -0700 From: To: , , , , Subject: [PATCH] eventfd: Enlarge recursion limit to allow vhost to work Date: Fri, 10 Apr 2020 19:47:20 +0800 Message-ID: <20200410114720.24838-1-zhe.he@windriver.com> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: He Zhe commit b5e683d5cab8 ("eventfd: track eventfd_signal() recursion depth") introduces a percpu counter that tracks the percpu recursion depth and warn if it greater than zero, to avoid potential deadlock and stack overflow. However sometimes different eventfds may be used in parallel. Specifically, when heavy network load goes through kvm and vhost, working as below, it would trigger the following call trace. - 100.00% - 66.51% ret_from_fork kthread - vhost_worker - 33.47% handle_tx_kick handle_tx handle_tx_copy vhost_tx_batch.isra.0 vhost_add_used_and_signal_n eventfd_signal - 33.05% handle_rx_net handle_rx vhost_add_used_and_signal_n eventfd_signal - 33.49% ioctl entry_SYSCALL_64_after_hwframe do_syscall_64 __x64_sys_ioctl ksys_ioctl do_vfs_ioctl kvm_vcpu_ioctl kvm_arch_vcpu_ioctl_run vmx_handle_exit handle_ept_misconfig kvm_io_bus_write __kvm_io_bus_write eventfd_signal 001: WARNING: CPU: 1 PID: 1503 at fs/eventfd.c:73 eventfd_signal+0x85/0xa0 ---- snip ---- 001: Call Trace: 001: vhost_signal+0x15e/0x1b0 [vhost] 001: vhost_add_used_and_signal_n+0x2b/0x40 [vhost] 001: handle_rx+0xb9/0x900 [vhost_net] 001: handle_rx_net+0x15/0x20 [vhost_net] 001: vhost_worker+0xbe/0x120 [vhost] 001: kthread+0x106/0x140 001: ? log_used.part.0+0x20/0x20 [vhost] 001: ? kthread_park+0x90/0x90 001: ret_from_fork+0x35/0x40 001: ---[ end trace 0000000000000003 ]--- This patch enlarges the limit to 1 which is the maximum recursion depth we have found so far. Signed-off-by: He Zhe --- fs/eventfd.c | 3 ++- include/linux/eventfd.h | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/eventfd.c b/fs/eventfd.c index 78e41c7c3d05..8b9bd6fb08cd 100644 --- a/fs/eventfd.c +++ b/fs/eventfd.c @@ -70,7 +70,8 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n) * it returns true, the eventfd_signal() call should be deferred to a * safe context. */ - if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count))) + if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count) > + EFD_WAKE_COUNT_MAX)) return 0; spin_lock_irqsave(&ctx->wqh.lock, flags); diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h index dc4fd8a6644d..e7684d768e3f 100644 --- a/include/linux/eventfd.h +++ b/include/linux/eventfd.h @@ -29,6 +29,9 @@ #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK) #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE) +/* This is the maximum recursion depth we find so far */ +#define EFD_WAKE_COUNT_MAX 1 + struct eventfd_ctx; struct file;