From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S970197AbdDUHAy (ORCPT <rfc822;w@1wt.eu>);
        Fri, 21 Apr 2017 03:00:54 -0400
Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:51681 "EHLO
        mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S968024AbdDUHAv (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 21 Apr 2017 03:00:51 -0400
Subject: Re: [PATCH 2/6] locking: Introduce range reader/writer lock
To: Davidlohr Bueso <dave@stgolabs.net>
References: <20170406084620.22700-1-dave@stgolabs.net>
 <20170406084620.22700-3-dave@stgolabs.net>
 <b1a53492-7fb3-a3cd-80d1-92dc4be5d8c4@linux.vnet.ibm.com>
 <20170420155125.GA20746@linux-80c1.suse>
Cc: mingo@kernel.org, peterz@infradead.org, akpm@linux-foundation.org,
        jack@suse.cz, kirill.shutemov@linux.intel.com, mhocko@suse.com,
        mgorman@techsingularity.net, linux-kernel@vger.kernel.org,
        Davidlohr Bueso <dbueso@suse.de>
From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Date: Fri, 21 Apr 2017 09:00:41 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.8.0
MIME-Version: 1.0
In-Reply-To: <20170420155125.GA20746@linux-80c1.suse>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
X-TM-AS-GCONF: 00
x-cbid: 17042107-0020-0000-0000-0000034CE405
X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused
x-cbparentid: 17042107-0021-0000-0000-0000415F347E
Message-Id: <d6378a2f-acf2-6771-970f-b0fbf2d3a120@linux.vnet.ibm.com>
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-21_06:,,
 signatures=0
X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0
 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam
 adjust=0 reason=mlx scancount=1 engine=8.0.1-1703280000
 definitions=main-1704210129
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 20/04/2017 18:01, Davidlohr Bueso wrote:
>>> +int range_read_trylock(struct range_rwlock_tree *tree, struct
>>> range_rwlock *lock)
>>> +{
>>> +    int ret = true;
>>> +    unsigned long flags;
>>> +    struct interval_tree_node *node;
>>> +
>>> +    spin_lock_irqsave(&tree->lock, flags);
>>> +
>>> +    if (!__range_intersects_intree(tree, lock))
>>> +        goto insert;
>>> +
>>> +    /*
>>> +     * We have overlapping ranges in the tree, ensure that we can
>>> +     * in fact share the lock.
>>> +     */
>>> +    range_interval_tree_foreach(node, &tree->root,
>>> +                    lock->node.start, lock->node.last) {
>>> +        struct range_rwlock *blocked_lock;
>>> +        blocked_lock = range_entry(node, struct range_rwlock, node);
>>> +
>>> +        if (!range_lock_is_reader(blocked_lock)) {
>>> +            ret = false;
>>> +            goto unlock;
>>> +        }
>>> +    }
>>> +insert:
>>> +    range_lock_set_reader(lock);
>>
>> Here, the lock->waiter field should have been set to current before
>> calling range_lock_set_reader()
> 
> But this is a trylock attempt, there is no waiting going on.

Agreed, this one is useless.