Subject: Re: [PATCH] Change the spin_lock/unlock_irq interface in
 proc_alloc_inum() function
To: Al Viro <viro@ZenIV.linux.org.uk>
References: <1456886879-28128-1-git-send-email-majun258@huawei.com>
 <20160302030941.GH17997@ZenIV.linux.org.uk>
CC: <ebiederm@xmission.com>, <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>, <akpm@linux-foundation.org>,
        <dhowells@redhat.com>, <Waiman.Long@hp.com>, <dingtianhong@huawei.com>,
        <guohanjun@huawei.com>, <fanjinke1@huawei.com>
From: "majun (F)" <majun258@huawei.com>
Message-ID: <56D688FC.9020202@huawei.com>
Date: Wed, 2 Mar 2016 14:32:28 +0800
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在 2016/3/2 11:09, Al Viro 写道:
> On Wed, Mar 02, 2016 at 10:47:59AM +0800, MaJun wrote:
>> From: Ma Jun <majun258@huawei.com>
>>
>> The spin_lock/unlock_irq interface is not safe when this function is called
>> at some case which need irq disabled.
> 
>> For example:
>> 	spin_lock_irqsave()
>> 	|
>> 	request_irq() --> proc_alloc_inum()
>> 	|
>> 	spin_unlock_irqrestore()
> 
> Do you even read your own patch?
> 
>>  	if (!ida_pre_get(&proc_inum_ida, GFP_KERNEL))
> 					 ^^^^^^^^^^
> 					 This.
> 
> It can block.  You *can't* call that under spin_lock_irqsave().  At all.
> You also can't do request_irq() under a spinlock, no matter whether you
> disable irqs or not - it also blocks.  So does proc_mkdir(), for that
> matter, and not only in proc_alloc_inum().
> 
> NAKed.  Don't do it.  request_irq() is not to be called under spinlocks,
> with or without irqs disabled.
> 

Sorry,I made a wrong example for this problem.
I want to say this interface may change the irq status after this function
be called.

Thanks!
MaJun

> .
>