Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753907AbaJQTTz (ORCPT ); Fri, 17 Oct 2014 15:19:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38536 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753805AbaJQTTy (ORCPT ); Fri, 17 Oct 2014 15:19:54 -0400 Date: Fri, 17 Oct 2014 21:16:43 +0200 From: Oleg Nesterov To: Andrew Morton , Martin Schwidefsky Cc: Tetsuo Handa , linux-kernel@vger.kernel.org, torvalds@linux-foundation.org Subject: [PATCH 2/2] usermodehelper: kill the kmod_thread_locker logic Message-ID: <20141017191643.GC22270@redhat.com> References: <20141016160042.7f898871@mschwide> <201410170157.AFH86961.FQtFHJVLOFSOOM@I-love.SAKURA.ne.jp> <20141016174209.GB18318@redhat.com> <201410170630.EBH48400.FSOHVQJOFMLtFO@I-love.SAKURA.ne.jp> <20141016215834.GA28864@redhat.com> <20141017093653.6fa60dff@mschwide> <20141017191557.GA22270@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141017191557.GA22270@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Now that we do not call kernel_thread(CLONE_VFORK) from the worker thread we can not deadlock if do_execve() in turn triggers another call_usermodehelper(), we can remove the kmod_thread_locker code. Note: we should probably kill khelper_wq and simply use one of the global workqueues, say, system_unbound_wq, this special wq for umh buys nothing nowadays. Signed-off-by: Oleg Nesterov --- kernel/kmod.c | 33 +++------------------------------ 1 files changed, 3 insertions(+), 30 deletions(-) diff --git a/kernel/kmod.c b/kernel/kmod.c index 4621771..2777f40 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -47,13 +47,6 @@ extern int max_threads; static struct workqueue_struct *khelper_wq; -/* - * kmod_thread_locker is used for deadlock avoidance. There is no explicit - * locking to protect this global - it is private to the singleton khelper - * thread and should only ever be modified by that thread. - */ -static const struct task_struct *kmod_thread_locker; - #define CAP_BSET (void *)1 #define CAP_PI (void *)2 @@ -273,13 +266,6 @@ out: do_exit(0); } -static int call_helper(void *data) -{ - /* Worker thread started blocking khelper thread. */ - kmod_thread_locker = current; - return ____call_usermodehelper(data); -} - /* Keventd can't block, but this (a child) can. */ static int wait_for_helper(void *data) { @@ -327,11 +313,9 @@ static void __call_usermodehelper(struct work_struct *work) if (sub_info->wait & UMH_WAIT_PROC) pid = kernel_thread(wait_for_helper, sub_info, CLONE_FS | CLONE_FILES | SIGCHLD); - else { - pid = kernel_thread(call_helper, sub_info, SIGCHLD); - /* Worker thread stopped blocking khelper thread. */ - kmod_thread_locker = NULL; - } + else + pid = kernel_thread(____call_usermodehelper, sub_info, + SIGCHLD); if (pid < 0) { sub_info->retval = pid; @@ -565,17 +549,6 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) goto out; } /* - * Worker thread must not wait for khelper thread at below - * wait_for_completion() if the thread was created with CLONE_VFORK - * flag, for khelper thread is already waiting for the thread at - * wait_for_completion() in do_fork(). - */ - if (wait != UMH_NO_WAIT && current == kmod_thread_locker) { - retval = -EBUSY; - goto out; - } - - /* * Set the completion pointer only if there is a waiter. * This makes it possible to use umh_complete to free * the data structure in case of UMH_NO_WAIT. -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/