Re: question on context of kfree_skb()

Manfred Spraul (
Tue, 31 Dec 2002 10:31:51 +0100

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.


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