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Date:   Wed, 25 Jul 2018 13:56:32 -0400 (EDT)
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
cc:     arnd@arndb.de, <gregkh@linuxfoundation.org>,
        <ulf.hansson@linaro.org>, <bauer.chen@realtek.com>,
        <ricky_wu@realtek.com>, <linux-kernel@vger.kernel.org>,
        <linux-usb@vger.kernel.org>
Subject: Re: [PATCH 2/5] memstick: Prevent memstick host from getting runtime
 suspended during card detection
In-Reply-To: <20180725152515.1833-3-kai.heng.feng@canonical.com>
Message-ID: <Pine.LNX.4.44L0.1807251353550.1467-100000@iolanthe.rowland.org>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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On Wed, 25 Jul 2018, Kai-Heng Feng wrote:

> We can use MEMSTICK_POWER_{ON,OFF} along with pm_runtime_{get,put}
> helpers to let memstick host support runtime pm.
> 
> There's a small window between memstick_detect_change() and its queued
> work, memstick_check(). In this window the rpm count may go down to zero
> before the memstick host powers on, so the host can be inadvertently
> suspended.
> 
> Increment rpm count before calling memstick_check(), and decrement rpm
> count afterward, as now we are sure the memstick host should be
> suspended or not.
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
>  drivers/memstick/core/memstick.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/memstick/core/memstick.c b/drivers/memstick/core/memstick.c
> index 76382c858c35..944fe0c93fa7 100644
> --- a/drivers/memstick/core/memstick.c
> +++ b/drivers/memstick/core/memstick.c
> @@ -18,6 +18,7 @@
>  #include <linux/delay.h>
>  #include <linux/slab.h>
>  #include <linux/module.h>
> +#include <linux/pm_runtime.h>
>  
>  #define DRIVER_NAME "memstick"
>  
> @@ -209,6 +210,7 @@ static int memstick_dummy_check(struct memstick_dev *card)
>   */
>  void memstick_detect_change(struct memstick_host *host)
>  {
> +	pm_runtime_get_noresume(host->dev.parent);
>  	queue_work(workqueue, &host->media_checker);
>  }
>  EXPORT_SYMBOL(memstick_detect_change);
> @@ -479,6 +481,8 @@ static void memstick_check(struct work_struct *work)
>  		host->set_param(host, MEMSTICK_POWER, MEMSTICK_POWER_OFF);
>  
>  	mutex_unlock(&host->lock);
> +
> +	pm_runtime_put_noidle(host->dev.parent);
>  	dev_dbg(&host->dev, "memstick_check finished\n");
>  }

This should be pm_runtime_put(), not _put_noidle().  The reason is
because if this call causes the PM runtime usage count to drop to 0,
you do want the device to go into runtime suspend.

Alan Stern