linux-kernel - Re: [PATCH v3] locking/pvqspinlock: restore/set vcpu_hashed state after failing adaptive locking spinning

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Message-ID: <CANRm+Cy-cOYPmEbaRFywysxc2vg5BpKR-UXsqzXA-sX1XBVeRw@mail.gmail.com>
Date:	Fri, 15 Jul 2016 05:26:40 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Waiman Long <waiman.long@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH v3] locking/pvqspinlock: restore/set vcpu_hashed state
 after failing adaptive locking spinning

2016-07-14 22:52 GMT+08:00 Waiman Long <waiman.long@....com>:
[...]
> As pv_kick_node() is called immediately after designating the next node as
> the queue head, the chance of this racing is possible, but is not likely
> unless the lock holder vCPU gets preempted for a long time at that right
> moment. This change does not do any harm though, so I am OK with that.
> However, I do want you to add a comment about the possible race in the code
> as it isn't that obvious or likely.

How about something like:

/*
 * If the lock holder vCPU gets preempted for a long time, pv_kick_node will
 * advance its state and hash the lock, restore/set the vcpu_hashed state to
 * avoid the race.
 */

Btw, do you think patch title should be improved, what do you like?

Regards,
Wanpeng Li