hi,
Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> On Fri, Sep 02, 2016 at 04:16:54PM -0400, Alan Stern wrote:
>> Felipe, your tests will show whether my guess was totally off-base.
>> For the new people, Felipe is tracking down a problem that involves
>> exactly the code sequence listed at the top of the email, where we know
>> that the wakeup routine runs but nevertheless the task sleeps. At
>> least, that's what it looks like at the moment.
>
> What arch are you seeing this on?
x86. Skylake to be exact.
The following change survived through the night:
diff --git a/drivers/usb/gadget/function/f_mass_storage.c b/drivers/usb/gadget/function/f_mass_storage.c
index 8f3659b65f53..d31581dd5ce5 100644
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -395,7 +395,7 @@ 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 */
+ smp_mb(); /* 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)
@@ -626,7 +626,7 @@ static int sleep_thread(struct fsg_common *common, bool can_freeze)
}
__set_current_state(TASK_RUNNING);
common->thread_wakeup_needed = 0;
- smp_rmb(); /* ensure the latest bh->state is visible */
+ smp_mb(); /* ensure the latest bh->state is visible */
return rc;
}
I'll keep it running until Monday at least
--
balbi
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