Messages in this thread | | | Date | Sat, 3 Sep 2016 14:31:33 +0200 | From | Peter Zijlstra <> | Subject | Re: Memory barrier needed with wake_up_process()? |
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On Fri, Sep 02, 2016 at 04:29:19PM -0400, Alan Stern wrote: > I'm afraid so. The code doesn't use wait_event(), in part because > there's no wait_queue (since only one task is involved).
You can use wait_queue fine with just one task, and it would clean up the code tremendously.
You can replace things like the earlier mentioned:
while (bh->state != BUF_STATE_EMPTY) { rc = sleep_thread(common, false); if (rc) return rc; }
with:
rc = wait_event_interruptible(&common->wq, bh->state == BUF_STATE_EMPTY); if (rc) return rc;
> But maybe there's another barrier which needs to be fixed. Felipe, can > you check to see if received_cbw() is getting called in > get_next_command(), and if so, what value it returns? Or is the > preceding sleep_thread() the one that never wakes up? > > It could be that the smp_wmb() in wakeup_thread() needs to be smp_mb(). > The reason being that get_next_command() runs outside the protection of > the spinlock.
Being somewhat confused by the code, I fail to follow that argument. wakeup_thread() is always called under that spinlock(), but since the critical section is 2 stores, I fail to see how a smp_mb() can make any difference over the smp_wmb() already there.
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