linux-kernel - Re: [PATCH V2] firmware loader: Fix the race FW_STATUS_DONE is followed by class

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Date:	Thu, 8 Nov 2012 10:01:35 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Chuansheng Liu <chuansheng.liu@...el.com>
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] firmware loader: Fix the race FW_STATUS_DONE is
 followed by class_timeout

On Thu, Nov 8, 2012 at 6:29 PM, Chuansheng Liu <chuansheng.liu@...el.com> wrote:
>
> There is a race as below when calling request_firmware():
> CPU1                                   CPU2
> write 0 > loading
> mutex_lock(&fw_lock)
> ...
> set_bit FW_STATUS_DONE                 class_timeout is coming
>                                        set_bit FW_STATUS_ABORT
> complete_all &completion
> ...
> mutex_unlock(&fw_lock)
>
> In this time, the bit FW_STATUS_DONE and FW_STATUS_ABORT are set,
> and request_firmware() will return failure due to condition in
> _request_firmware_load():
>         if (!buf->size || test_bit(FW_STATUS_ABORT, &buf->status))
>                 retval = -ENOENT;
>
> But from the above scenerio, it should be a successful requesting.
> So we need judge if the bit FW_STATUS_DONE is already set before
> calling fw_load_abort() in timeout function.
>
> As Ming's proposal, we need change the timer into sched_work to
> benefit from using &fw_lock mutex also.
>
> Signed-off-by: liu chuansheng <chuansheng.liu@...el.com>
> ---
>  drivers/base/firmware_class.c |   25 +++++++++++++++++--------
>  1 files changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index 8945f4e..f2caa0a 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -143,7 +143,7 @@ struct fw_cache_entry {
>  };
>
>  struct firmware_priv {
> -       struct timer_list timeout;
> +       struct delayed_work timeout_work;
>         bool nowait;
>         struct device dev;
>         struct firmware_buf *buf;
> @@ -667,10 +667,17 @@ static struct bin_attribute firmware_attr_data = {
>         .write = firmware_data_write,
>  };
>
> -static void firmware_class_timeout(u_long data)
> +static void firmware_class_timeout_work(struct work_struct *work)
>  {
> -       struct firmware_priv *fw_priv = (struct firmware_priv *) data;
> +       struct firmware_priv *fw_priv = container_of(work,
> +                       struct firmware_priv, timeout_work.work);
>
> +       mutex_lock(&fw_lock);
> +       if (test_bit(FW_STATUS_DONE, &(fw_priv->buf->status))) {
> +               mutex_unlock(&fw_lock);
> +               return;
> +       }
> +       mutex_unlock(&fw_lock);
>         fw_load_abort(fw_priv);

fw_lock should be held when fw_load_abort(fw_priv) is running.

>  }
>
> @@ -690,8 +697,8 @@ fw_create_instance(struct firmware *firmware, const char *fw_name,
>
>         fw_priv->nowait = nowait;
>         fw_priv->fw = firmware;
> -       setup_timer(&fw_priv->timeout,
> -                   firmware_class_timeout, (u_long) fw_priv);
> +       INIT_DELAYED_WORK(&fw_priv->timeout_work,
> +               firmware_class_timeout_work);
>
>         f_dev = &fw_priv->dev;
>
> @@ -858,7 +865,9 @@ static int _request_firmware_load(struct firmware_priv *fw_priv, bool uevent,
>                 dev_dbg(f_dev->parent, "firmware: direct-loading"
>                         " firmware %s\n", buf->fw_id);
>
> +               mutex_lock(&fw_lock);
>                 set_bit(FW_STATUS_DONE, &buf->status);
> +               mutex_unlock(&fw_lock);
>                 complete_all(&buf->completion);
>                 direct_load = 1;
>                 goto handle_fw;
> @@ -894,15 +903,15 @@ static int _request_firmware_load(struct firmware_priv *fw_priv, bool uevent,
>                 dev_set_uevent_suppress(f_dev, false);
>                 dev_dbg(f_dev, "firmware: requesting %s\n", buf->fw_id);
>                 if (timeout != MAX_SCHEDULE_TIMEOUT)
> -                       mod_timer(&fw_priv->timeout,
> -                                 round_jiffies_up(jiffies + timeout));
> +                       schedule_delayed_work(&fw_priv->timeout_work,
> +                                       timeout * HZ);

timeout is in unit of jiffies already, so multiplying by 'HZ' isn't needed.

>
>                 kobject_uevent(&fw_priv->dev.kobj, KOBJ_ADD);
>         }
>
>         wait_for_completion(&buf->completion);
>
> -       del_timer_sync(&fw_priv->timeout);
> +       cancel_delayed_work_sync(&fw_priv->timeout_work);
>
>  handle_fw:
>         mutex_lock(&fw_lock);
> --
> 1.7.0.4
>
>
>

Thanks,
--
Ming Lei
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