Peter Hurley wrote:
> On 10/09/2015 01:28 PM, Peter Hurley wrote:
>> Tatsukawa-san,
>>
>> I would still like to root-cause the reported stall; is the reported
>> stall resolved if smp_mb() is added before the waitqueue_active()
>> in __receive_buf()?
>
> Nevermind, I see it now.
>
> The store to commit_head is deferred until after the load of read_wait->next;
> a full memory barrier would properly order the store before the load but,
> since that is roughly equivalent to taking the spin lock for the wake up
> anyway,
> it makes sense to just always do the wakeup.
The stall problem is resolved if smp_mb() is added both before the
waitqueue_active() in __receive_buf(), and before the line containing
input_available_p() in n_tty_read().
---
Kosuke TATSUKAWA | 3rd IT Platform Department
| IT Platform Division, NEC Corporation
| ta...@ab.jp.nec.com
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