Re: [PATCH] usb: gadget: f_mass_storage: add missing memory barrier for thread_wakeup_needed

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On Fri, Mar 15 2013, UCHINO Satoshi <satoshi.uchino@xxxxxxxxxxxxx> wrote:
> Without this memory barrier, the file-storage thread may fail to
> escape from the following while loop, because it may observe new
> common->thread_wakeup_needed and old bh->state which are updated by
> the callback functions.
>
> 	/* Wait for the CBW to arrive */
> 	while (bh->state != BUF_STATE_FULL) {
> 		rc = sleep_thread(common);
> 		if (rc)
> 			return rc;
> 	}
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: UCHINO Satoshi <satoshi.uchino@xxxxxxxxxxxxx>
> ---
>  drivers/usb/gadget/f_mass_storage.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/usb/gadget/f_mass_storage.c b/drivers/usb/gadget/f_mass_storage.c
> index fc5c16c..0b6d351 100644
> --- a/drivers/usb/gadget/f_mass_storage.c
> +++ b/drivers/usb/gadget/f_mass_storage.c
> @@ -414,6 +414,7 @@ static int fsg_set_halt(struct fsg_dev *fsg, struct usb_ep *ep)
>  static void wakeup_thread(struct fsg_common *common)
>  {
>  	/* Tell the main thread that something has happened */
> +	smp_wmb();
>  	common->thread_wakeup_needed = 1;
>  	if (common->thread_task)
>  		wake_up_process(common->thread_task);
> @@ -632,6 +633,7 @@ static int sleep_thread(struct fsg_common *common)
>  	}
>  	__set_current_state(TASK_RUNNING);
>  	common->thread_wakeup_needed = 0;
> +	smp_rmb();
>  	return rc;
>  }

In both places, add comment describing why the barrier is needed.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@xxxxxxxxxx>--------------ooO--(_)--Ooo--

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