linux-kernel - Re: [Xen-devel] [PATCH 2/6] xenbus: implement the xenwatch multithreading framework

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Date:   Mon, 17 Sep 2018 16:00:19 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     jgross@...e.com, wei.liu2@...rix.com, konrad.wilk@...cle.com,
        srinivas.eeda@...cle.com, paul.durrant@...rix.com,
        roger.pau@...rix.com
Subject: Re: [Xen-devel] [PATCH 2/6] xenbus: implement the xenwatch
 multithreading framework

On 9/16/18 9:48 PM, Dongli Zhang wrote:
> Hi Boris,
>
> On 09/17/2018 05:20 AM, Boris Ostrovsky wrote:
>>
>> On 9/14/18 3:34 AM, Dongli Zhang wrote:
>>> +
>>> +/* Running in the context of default xenwatch kthread. */
>>> +void mtwatch_create_domain(domid_t domid)
>>> +{
>>> +    struct mtwatch_domain *domain;
>>> +
>>> +    if (!domid) {
>>> +        pr_err("Default xenwatch thread is for dom0\n");
>>> +        return;
>>> +    }
>>> +
>>> +    spin_lock(&mtwatch_info->domain_lock);
>>> +
>>> +    domain = mtwatch_find_domain(domid);
>>> +    if (domain) {
>>> +        atomic_inc(&domain->refcnt);
>>> +        spin_unlock(&mtwatch_info->domain_lock);
>>> +        return;
>>> +    }
>>> +
>>> +    domain = kzalloc(sizeof(*domain), GFP_ATOMIC);
>> Is there a reason (besides this being done under spinlock) for using GFP_ATOMIC?
>> If domain_lock is the only reason I'd probably drop the lock and do GFP_KERNEL.
> spin_lock is the reason.
>
> Would you like to switch to a mutex here?

I'd use mutex.

-boris