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Message-ID: <3E116407.6040802@colorfullife.com>
Date: Tue, 31 Dec 2002 10:31:51 +0100
From: Manfred Spraul <manfred@colorfullife.com>
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To: Oliver Neukum <oliver@neukum.name>
CC: Muli Ben-Yehuda <mulix@mulix.org>, linux-kernel@vger.kernel.org
Subject: Re: question on context of kfree_skb()
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Oliver Neukum wrote:

>Am Montag, 30. Dezember 2002 23:32 schrieb Manfred Spraul:
>  
>
>>Mulix wrote:
>>    
>>
>>>dev_kfree_skb_any() should be called when you could be either
>>>executing in interrupt context or not.
>>>      
>>>
>>dev_kfree_skb_any() can misdetect the context: You must not use the
>>function if you hold an irq spinlock and you might be running from BH or
>>process context.
>>    
>>
>
>What then shall be used under these circumstances ?
>Could you perhaps summarise the issue ?
>  
>
When a packet is freed, the upper layers must be notified, for example a 
user space process could be waiting for socket buffer space. This can 
happen either immediately, or in the next softirq.

dev_kfree_skb_irq() is always ok, although slower than the other 
functions. The packet is unconditionally queued and processed later.
dev_kfree_skb_any() tries to optimize it a bit: If it thinks that it's 
save to process it now, then the packet is processed immediately. The 
autodetection is usually correct, except for the special case I 
mentioned. Drivers must work around that.
dev_kfree_skb() always processes the packet immediately. Only permitted 
from bottom half context or from process context.

--
    Manfred

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