From patchwork Fri Dec 10 16:10:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Rafael J. Wysocki" X-Patchwork-Id: 522972 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59663C433EF for ; Fri, 10 Dec 2021 16:10:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238157AbhLJQNw (ORCPT ); Fri, 10 Dec 2021 11:13:52 -0500 Received: from cloudserver094114.home.pl ([79.96.170.134]:43522 "EHLO cloudserver094114.home.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240110AbhLJQNv (ORCPT ); Fri, 10 Dec 2021 11:13:51 -0500 Received: from localhost (127.0.0.1) (HELO v370.home.net.pl) by /usr/run/smtp (/usr/run/postfix/private/idea_relay_lmtp) via UNIX with SMTP (IdeaSmtpServer 3.0.1) id 67377897416ad859; Fri, 10 Dec 2021 17:10:15 +0100 Received: from kreacher.localnet (unknown [213.134.162.58]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by v370.home.net.pl (Postfix) with ESMTPSA id 78DEB66AD3B; Fri, 10 Dec 2021 17:10:14 +0100 (CET) From: "Rafael J. Wysocki" To: Linux PM Cc: Peter Zijlstra , LKML , Ulf Hansson , Greg Kroah-Hartman Subject: [PATCH] PM: runtime: Add safety net to supplier device release Date: Fri, 10 Dec 2021 17:10:13 +0100 Message-ID: <11889065.O9o76ZdvQC@kreacher> MIME-Version: 1.0 X-CLIENT-IP: 213.134.162.58 X-CLIENT-HOSTNAME: 213.134.162.58 X-VADE-SPAMSTATE: clean X-VADE-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedvuddrkedvgdekhecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfjqffogffrnfdpggftiffpkfenuceurghilhhouhhtmecuudehtdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhephffvufffkfgggfgtsehtufertddttdejnecuhfhrohhmpedftfgrfhgrvghlucflrdcuhgihshhotghkihdfuceorhhjfiesrhhjfiihshhotghkihdrnhgvtheqnecuggftrfgrthhtvghrnhephfegtdffjeehkeegleejveevtdeugfffieeijeduuddtkefgjedvheeujeejtedvnecukfhppedvudefrddufeegrdduiedvrdehkeenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepihhnvghtpedvudefrddufeegrdduiedvrdehkedphhgvlhhopehkrhgvrggthhgvrhdrlhhotggrlhhnvghtpdhmrghilhhfrhhomhepfdftrghfrggvlhculfdrucghhihsohgtkhhifdcuoehrjhifsehrjhifhihsohgtkhhirdhnvghtqedprhgtphhtthhopehlihhnuhigqdhpmhesvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehpvghtvghriiesihhnfhhrrgguvggrugdrohhrghdprhgtphhtthhopehlihhnuhigqdhkvghrnhgvlhesvhhgvghrrdhkvghrnhgvlhdrohhrghdprhgtphhtthhopehulhhfrdhhrghnshhsohhnsehlihhnrghrohdrohhrghdprhgtphhtthhopehgrhgvghhkhheslhhinhhugihfohhunhgurght ihhonhdrohhrgh X-DCC--Metrics: v370.home.net.pl 1024; Body=5 Fuz1=5 Fuz2=5 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org From: Rafael J. Wysocki Because refcount_dec_not_one() returns true if the target refcount becomes saturated, it is generally unsafe to use its return value as a loop termination condition, but that is what happens when a device link's supplier device is released during runtime PM suspend operations and on device link removal. To address this, introduce pm_runtime_release_supplier() to be used in the above cases which will check the supplier device's runtime PM usage counter in addition to the refcount_dec_not_one() return value, so the loop can be terminated in case the rpm_active refcount value becomes invalid, and update the code in question to use it as appropriate. This change is not expected to have any visible functional impact. Reported-by: Peter Zijlstra Signed-off-by: Rafael J. Wysocki Acked-by: Peter Zijlstra (Intel) --- drivers/base/core.c | 3 +-- drivers/base/power/runtime.c | 41 ++++++++++++++++++++++++++++++----------- include/linux/pm_runtime.h | 3 +++ 3 files changed, 34 insertions(+), 13 deletions(-) Index: linux-pm/drivers/base/power/runtime.c =================================================================== --- linux-pm.orig/drivers/base/power/runtime.c +++ linux-pm/drivers/base/power/runtime.c @@ -305,19 +305,40 @@ static int rpm_get_suppliers(struct devi return 0; } +/** + * pm_runtime_release_supplier - Drop references to device link's supplier. + * @link: Target device link. + * @check_idle: Whether or not to check if the supplier device is idle. + * + * Drop all runtime PM references associated with @link to its supplier device + * and if @check_idle is set, check if that device is idle (and so it can be + * suspended). + */ +void pm_runtime_release_supplier(struct device_link *link, bool check_idle) +{ + struct device *supplier = link->supplier; + + /* + * The additional power.usage_count check is a safety net in case + * the rpm_active refcount becomes saturated, in which case + * refcount_dec_not_one() would return true forever, but it is not + * strictly necessary. + */ + while (refcount_dec_not_one(&link->rpm_active) && + atomic_read(&supplier->power.usage_count) > 0) + pm_runtime_put_noidle(supplier); + + if (check_idle) + pm_request_idle(supplier); +} + static void __rpm_put_suppliers(struct device *dev, bool try_to_suspend) { struct device_link *link; list_for_each_entry_rcu(link, &dev->links.suppliers, c_node, - device_links_read_lock_held()) { - - while (refcount_dec_not_one(&link->rpm_active)) - pm_runtime_put_noidle(link->supplier); - - if (try_to_suspend) - pm_request_idle(link->supplier); - } + device_links_read_lock_held()) + pm_runtime_release_supplier(link, try_to_suspend); } static void rpm_put_suppliers(struct device *dev) @@ -1777,9 +1798,7 @@ void pm_runtime_drop_link(struct device_ return; pm_runtime_drop_link_count(link->consumer); - - while (refcount_dec_not_one(&link->rpm_active)) - pm_runtime_put(link->supplier); + pm_runtime_release_supplier(link, true); } static bool pm_runtime_need_not_resume(struct device *dev) Index: linux-pm/include/linux/pm_runtime.h =================================================================== --- linux-pm.orig/include/linux/pm_runtime.h +++ linux-pm/include/linux/pm_runtime.h @@ -58,6 +58,7 @@ extern void pm_runtime_get_suppliers(str extern void pm_runtime_put_suppliers(struct device *dev); extern void pm_runtime_new_link(struct device *dev); extern void pm_runtime_drop_link(struct device_link *link); +extern void pm_runtime_release_supplier(struct device_link *link, bool check_idle); extern int devm_pm_runtime_enable(struct device *dev); @@ -283,6 +284,8 @@ static inline void pm_runtime_get_suppli static inline void pm_runtime_put_suppliers(struct device *dev) {} static inline void pm_runtime_new_link(struct device *dev) {} static inline void pm_runtime_drop_link(struct device_link *link) {} +static inline void pm_runtime_release_supplier(struct device_link *link, + bool check_idle) {} #endif /* !CONFIG_PM */ Index: linux-pm/drivers/base/core.c =================================================================== --- linux-pm.orig/drivers/base/core.c +++ linux-pm/drivers/base/core.c @@ -485,8 +485,7 @@ static void device_link_release_fn(struc /* Ensure that all references to the link object have been dropped. */ device_link_synchronize_removal(); - while (refcount_dec_not_one(&link->rpm_active)) - pm_runtime_put(link->supplier); + pm_runtime_release_supplier(link, true); put_device(link->consumer); put_device(link->supplier);