On Mon, Mar 18 2013, UCHINO Satoshi 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: sta...@vger.kernel.org
> Signed-off-by: UCHINO Satoshi <satoshi.uch...@toshiba.co.jp>
Acked-by: Michal Nazarewicz <min...@mina86.com>
> ---
> Changes in v2:
> - add comments why the barrier is needed
>
> 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 97666e8..c35a9ec 100644
> --- a/drivers/usb/gadget/f_mass_storage.c
> +++ b/drivers/usb/gadget/f_mass_storage.c
> @@ -413,6 +413,7 @@ static int fsg_set_halt(struct fsg_dev *fsg, struct
> usb_ep *ep)
> /* Caller must hold fsg->lock */
> static void wakeup_thread(struct fsg_common *common)
> {
> + smp_wmb(); /* ensure the write of bh->state is complete */
> /* Tell the main thread that something has happened */
> common->thread_wakeup_needed = 1;
> if (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(); /* ensure the latest bh->state is visible */
> return rc;
> }
>
> --
> 1.7.4.1
>
--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michał “mina86” Nazarewicz (o o)
ooo +----<email/xmpp: m...@google.com>--------------ooO--(_)--Ooo--
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