linux-kernel - Re: [PATCH 2/2] xen: xenbus: WARN_ON XS_TRANSACTION

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Date:   Sun, 11 Feb 2018 10:28:38 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Simon Gaiser <simon@...isiblethingslab.com>,
        xen-devel@...ts.xenproject.org
Cc:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] xen: xenbus: WARN_ON XS_TRANSACTION_{START,END}
 misuse



On 02/10/2018 08:27 PM, Simon Gaiser wrote:
> Boris Ostrovsky:
>> On 02/07/2018 05:22 PM, Simon Gaiser wrote:
>>> +    users_old = xs_state_users;
>>>        xs_state_users--;
>>>        if ((req->type == XS_TRANSACTION_START && req->msg.type == XS_ERROR) ||
>>>            req->type == XS_TRANSACTION_END)
>>>            xs_state_users--;
>>> +    if (WARN_ON(xs_state_users > users_old))
>>
>>
>> WARN_ON_ONCE()?
> 
> Since we "fix" the wrong decrement by clamping at zero it should not
> happen immediately again. But if you prefer _ONCE I can change it.
> 


If this error can happen once then someone at least theoretically can 
construct a case when it is repeated. So let's switch to _ONCE() variant.

Thanks.
-boris