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SubjectRe: [PATCH] firmware loader: Fix the race FW_STATUS_DONE is followed by class_timeout
From
On Thu, Nov 8, 2012 at 12:45 AM, Chuansheng Liu
<chuansheng.liu@intel.com> wrote:
>
> There is a race condition 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)

Good catch, but your fix isn't correct.

>
> 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 succcessful requesting.
> So we need judge if the FW_STATUS_DONE is set before calling abort
> in timeout function firmware_class_timeout().
>
> Signed-off-by: liu chuansheng <chuansheng.liu@intel.com>
> ---
> drivers/base/firmware_class.c | 7 +++++++
> 1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
> index 8945f4e..35fffd8 100644
> --- a/drivers/base/firmware_class.c
> +++ b/drivers/base/firmware_class.c
> @@ -671,6 +671,13 @@ static void firmware_class_timeout(u_long data)
> {
> struct firmware_priv *fw_priv = (struct firmware_priv *) data;
>
> + mutex_lock(&fw_lock);

mutex can't be used in interrupt context, so one candidate fix is
to convert the timeout timer into delayed work, and hold the
'fw_lock' during the work function.

> + if (test_bit(FW_STATUS_DONE, &(fw_priv->buf->status))) {
> + mutex_unlock(&fw_lock);
> + return;
> + }
> + mutex_unlock(&fw_lock);
> +
> fw_load_abort(fw_priv);
> }

Also the lock of 'fw_lock' should be held when setting 'FW_STATUS_DONE'
in _request_firmware_load().

Could you send out a new patch to fix the race?

Thanks,
--
Ming Lei


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