Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756057AbdGLJai (ORCPT ); Wed, 12 Jul 2017 05:30:38 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:46728 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754512AbdGLJag (ORCPT ); Wed, 12 Jul 2017 05:30:36 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org DAB7A61290 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=tirupath@codeaurora.org From: Tirupathi Reddy To: broonie@kernel.org, lgirdwood@gmail.com Cc: linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, Tirupathi Reddy Subject: [PATCH 1/1] regulator: core: fix a possible race in disable_work handling Date: Wed, 12 Jul 2017 14:59:47 +0530 Message-Id: <1499851787-31016-1-git-send-email-tirupath@codeaurora.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3318 Lines: 83 A race condition between queueing and processing the disable_work instances results in having a work instance in the queue and the deferred_disables variable of regulator device structure having a value '0'. If no new regulator_disable_deferred() call later from clients, the deferred_disables variable value remains '0' and hits BUG() in regulator_disable_work() when the queued instance scheduled for processing the work. The race occurs as below: Core-0 Core-1 ..... /* deferred_disables = 2 */ ..... ..... /* disable_work is queued */ ..... ..... ..... regulator_disable_deferred: regulator_disable_work: mutex_lock(&rdev->mutex); ..... rdev->deferred_disables++; mutex_lock(&rdev->mutex); mutex_unlock(&rdev->mutex); ..... queue_delayed_work(...) count =rdev->deferred_disables; ..... rdev->deferred_disables = 0; ..... ..... ..... mutex_unlock(&rdev->mutex); ..... ..... ..... return; ..... ..... /* No new regulator_disable_deferred() calls from clients */ /* The newly queued instance is scheduled for processing */ ..... ..... regulator_disable_work: ..... mutex_lock(&rdev->mutex); BUG_ON(!rdev->deferred_disables); /* deferred_disables = 0 */ The race is fixed by removing the work instance that is queued while processing the previous queued instance. Cancel the newly queued instance from disable_work() handler just after reset the deferred_disables variable to value '0'. Also move the work queueing step before mutex_unlock in regulator_disable_deferred(). Also use mod_delayed_work() in the pace of queue_delayed_work() as queue_delayed_work() always uses the delay requested in the first call when multiple consumers call regulator_disable_deferred() close in time and does not guarantee the semantics of regulator_disable_deferred(). Signed-off-by: Tirupathi Reddy --- drivers/regulator/core.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c index e567fa5..9f4d484 100644 --- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -2396,6 +2396,14 @@ static void regulator_disable_work(struct work_struct *work) count = rdev->deferred_disables; rdev->deferred_disables = 0; + /* + * Workqueue functions queue the new work instance while the previous + * work instance is being processed. Cancel the queued work instance + * as the work instance under processing does the job of the queued + * work instance. + */ + cancel_delayed_work(&rdev->disable_work); + for (i = 0; i < count; i++) { ret = _regulator_disable(rdev); if (ret != 0) @@ -2439,10 +2447,10 @@ int regulator_disable_deferred(struct regulator *regulator, int ms) mutex_lock(&rdev->mutex); rdev->deferred_disables++; + mod_delayed_work(system_power_efficient_wq, &rdev->disable_work, + msecs_to_jiffies(ms)); mutex_unlock(&rdev->mutex); - queue_delayed_work(system_power_efficient_wq, &rdev->disable_work, - msecs_to_jiffies(ms)); return 0; } EXPORT_SYMBOL_GPL(regulator_disable_deferred); -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation