Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752337AbcLHTs6 (ORCPT ); Thu, 8 Dec 2016 14:48:58 -0500 Received: from mail.kernel.org ([198.145.29.136]:45748 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752126AbcLHTs4 (ORCPT ); Thu, 8 Dec 2016 14:48:56 -0500 From: "Luis R. Rodriguez" To: shuah@kernel.org, jeyu@redhat.com, rusty@rustcorp.com.au, ebiederm@xmission.com, dmitry.torokhov@gmail.com, acme@redhat.com, corbet@lwn.net Cc: martin.wilck@suse.com, mmarek@suse.com, pmladek@suse.com, hare@suse.com, rwright@hpe.com, jeffm@suse.com, DSterba@suse.com, fdmanana@suse.com, neilb@suse.com, linux@roeck-us.net, rgoldwyn@suse.com, subashab@codeaurora.org, xypron.glpk@gmx.de, keescook@chromium.org, atomlin@redhat.com, mbenes@suse.cz, paulmck@linux.vnet.ibm.com, dan.j.williams@intel.com, jpoimboe@redhat.com, davem@davemloft.net, mingo@redhat.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, "Luis R. Rodriguez" Subject: [RFC 06/10] kmod: provide sanity check on kmod_concurrent access Date: Thu, 8 Dec 2016 11:48:50 -0800 Message-Id: <20161208194850.2627-1-mcgrof@kernel.org> X-Mailer: git-send-email 2.10.2 In-Reply-To: <20161208184801.1689-1-mcgrof@kernel.org> References: <20161208184801.1689-1-mcgrof@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1335 Lines: 52 Only decrement *iff* we're possitive. Warn if we've hit a situation where the counter is already 0 after we're done with a modprobe call, this would tell us we have an unaccounted counter access -- this in theory should not be possible as only one routine controls the counter, however preemption is one case that could trigger this situation. Avoid that situation by disabling preemptiong while we access the counter. Signed-off-by: Luis R. Rodriguez --- kernel/kmod.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/kernel/kmod.c b/kernel/kmod.c index ab38539f7e91..09cf35a2075a 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -113,16 +113,28 @@ static int call_modprobe(char *module_name, int wait) static int kmod_umh_threads_get(void) { + int ret = 0; + + preempt_disable(); atomic_inc(&kmod_concurrent); if (atomic_read(&kmod_concurrent) < max_modprobes) - return 0; - atomic_dec(&kmod_concurrent); - return -EBUSY; + goto out; + + atomic_dec_if_positive(&kmod_concurrent); + ret = -EBUSY; +out: + preempt_enable(); + return 0; } static void kmod_umh_threads_put(void) { - atomic_dec(&kmod_concurrent); + int ret; + + preempt_disable(); + ret = atomic_dec_if_positive(&kmod_concurrent); + WARN_ON(ret < 0); + preempt_enable(); } /** -- 2.10.1