linux-kernel - Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160212221444.GC16417@linux-uzut.site>
Date:	Fri, 12 Feb 2016 14:14:44 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Waiman Long <Waiman.Long@....com>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ding Tianhong <dingtianhong@...wei.com>,
	Jason Low <jason.low2@....com>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <Will.Deacon@....com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Waiman Long <Waiman.Long@...com>
Subject: Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to
 mutex_optimistic_spin()

On Fri, 12 Feb 2016, Peter Zijlstra wrote:

>On Fri, Feb 12, 2016 at 12:32:12PM -0500, Waiman Long wrote:
>>  static bool mutex_optimistic_spin(struct mutex *lock,
>> +				  struct ww_acquire_ctx *ww_ctx,
>> +				  const bool use_ww_ctx, int waiter)
>>  {
>>  	struct task_struct *task = current;
>> +	bool acquired = false;
>>
>> +	if (!waiter) {
>> +		if (!mutex_can_spin_on_owner(lock))
>> +			goto done;
>
>Why doesn't the waiter have to check mutex_can_spin_on_owner() ?

afaict because mutex_can_spin_on_owner() fails immediately when the counter
is -1, which is a nono for the waiters case.

Thanks,
Davidlohr