From patchwork Sun Oct 17 17:22:09 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jonathan Cameron X-Patchwork-Id: 12564483 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ECDD3C433EF for ; Sun, 17 Oct 2021 17:18:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA9DE61038 for ; Sun, 17 Oct 2021 17:18:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344363AbhJQRUN (ORCPT ); Sun, 17 Oct 2021 13:20:13 -0400 Received: from mail.kernel.org ([198.145.29.99]:47040 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344366AbhJQRUL (ORCPT ); Sun, 17 Oct 2021 13:20:11 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 35E1560FE3; Sun, 17 Oct 2021 17:17:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1634491080; bh=vzJZdhchxdzgZYgOggisR+vt1rHb5f9gyspnV72jlnU=; h=From:To:Cc:Subject:Date:From; b=GF5KLZHLYFRgvAPTnpuIfdtDjGWoB05pfI1wfOnEZ/6+rOi1UEfZYghzyz+IBkdEW LtHOUhqzrLMawb/anqsCc329Fs5F0RxG3qt/o0SS5T6LA3tDPq3276zruvXkOUN9OO ZbHzhikyqIM+ZYThls/dENMPcJeAMwYPw6xTJGYp/JxoIxyNXgJDnClNQ4Do7ZydHA 8enmt8j/jpOq3DxuwoyAVUg+rqbBtbzWT8aZ2pizzasYtIldMi/sHxHrCGzh4JSygK EzPJvqqLlaSGMLKqCHi7IVSVv/LhiEfOSV5XHvX8lAjzUJyHrEHocyO3yK3mPsapJc FhHqClkhsWALg== From: Jonathan Cameron To: linux-iio@vger.kernel.org Cc: Jonathan Cameron , Oleksij Rempel , Pengutronix Kernel Team , Dmitry Torokhov Subject: [RFC PATCH] iio: trigger: Fix a scheduling whilst atomic issue seen on tsc2046 Date: Sun, 17 Oct 2021 18:22:09 +0100 Message-Id: <20211017172209.112387-1-jic23@kernel.org> X-Mailer: git-send-email 2.33.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-iio@vger.kernel.org From: Jonathan Cameron IIO triggers are software IRQ chips that split an incoming IRQ into separate IRQs routed to all devices using the trigger. When all consumers are done then a trigger callback reenable() is called. There are a few circumstances under which this can happen in atomic context. 1) A single user of the trigger that calls the iio_trigger_done() function from interrupt context. 2) A race between disconnecting the last device from a trigger and the trigger itself sucessfully being disabled. To avoid a resulting scheduling whilst atomic, close this corner by using schedule_work() to ensure the reenable is not done in atomic context. Note that drivers must be careful to manage the interaction of set_state() and reenable() callbacks to ensure appropriate reference counting if they are relying on the same hardware controls. Completely untested beyond building. Given it is Sunday evening very high chance of it being entirely wrong. The potential race conditions around this were giving me a headache, but I think this is at least a step in the right direction and should work for Oleksij's case. Signed-off-by: Jonathan Cameron Cc: Oleksij Rempel Cc: Pengutronix Kernel Team Cc: Dmitry Torokhov Tested-by: Oleksij Rempel --- drivers/iio/industrialio-trigger.c | 36 +++++++++++++++++++++++++++++- include/linux/iio/trigger.h | 2 ++ 2 files changed, 37 insertions(+), 1 deletion(-) diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c index b23caa2f2aa1..d3bdc9800b4a 100644 --- a/drivers/iio/industrialio-trigger.c +++ b/drivers/iio/industrialio-trigger.c @@ -162,6 +162,39 @@ static struct iio_trigger *iio_trigger_acquire_by_name(const char *name) return trig; } +static void iio_reenable_work_fn(struct work_struct *work) +{ + struct iio_trigger *trig = container_of(work, struct iio_trigger, + reenable_work); + + /* + * This 'might' occur after the trigger state is set to disabled - + * in that case the driver should skip reenabling. + */ + trig->ops->reenable(trig); +} + +/* + * In general, reenable callbacks may need to sleep and this path is + * not performance sensitive, so just queue up a work item + * to reneable the trigger for us. + * + * Races that can cause this. + * 1) A handler occurs entirely in interrupt context so the counter + * the final decrement is still in this interrupt. + * 2) The trigger has been removed, but one last interrupt gets through. + * + * For (1) we must call reenable, but not in atomic context. + * For (2) it should be safe to call reenanble, if drivers never blindly + * reenable after state is off. + */ +static void iio_trigger_notify_done_atomic(struct iio_trigger *trig) +{ + if (atomic_dec_and_test(&trig->use_count) && trig->ops && + trig->ops->reenable) + schedule_work(&trig->reenable_work); +} + void iio_trigger_poll(struct iio_trigger *trig) { int i; @@ -173,7 +206,7 @@ void iio_trigger_poll(struct iio_trigger *trig) if (trig->subirqs[i].enabled) generic_handle_irq(trig->subirq_base + i); else - iio_trigger_notify_done(trig); + iio_trigger_notify_done_atomic(trig); } } } @@ -535,6 +568,7 @@ struct iio_trigger *viio_trigger_alloc(struct device *parent, trig->dev.type = &iio_trig_type; trig->dev.bus = &iio_bus_type; device_initialize(&trig->dev); + INIT_WORK(&trig->reenable_work, iio_reenable_work_fn); mutex_init(&trig->pool_lock); trig->subirq_base = irq_alloc_descs(-1, 0, diff --git a/include/linux/iio/trigger.h b/include/linux/iio/trigger.h index 096f68dd2e0c..4c69b144677b 100644 --- a/include/linux/iio/trigger.h +++ b/include/linux/iio/trigger.h @@ -55,6 +55,7 @@ struct iio_trigger_ops { * @attached_own_device:[INTERN] if we are using our own device as trigger, * i.e. if we registered a poll function to the same * device as the one providing the trigger. + * @reenable_work: [INTERN] work item used to ensure reenable can sleep. **/ struct iio_trigger { const struct iio_trigger_ops *ops; @@ -74,6 +75,7 @@ struct iio_trigger { unsigned long pool[BITS_TO_LONGS(CONFIG_IIO_CONSUMERS_PER_TRIGGER)]; struct mutex pool_lock; bool attached_own_device; + struct work_struct reenable_work; };