if_start running deferred for Giant

Robert Watson rwatson at FreeBSD.org
Sun Dec 30 16:29:49 PST 2007

On Mon, 31 Dec 2007, Tofig Suleymanov wrote:

>>> xxxxxx kernel: ib0: if_start running deferred for Giant
>>> I am not sure what does this exactly mean.
>>> Any help would be appreciated.
>> This occurs when a network device driver has declared itself IFF_NEEDSGIANT 
>> -- that is, has declared that it requires the Giant lock in order to 
>> operate. As this is considered an undesirable state of affairs for a device 
>> driver, a warning is printed. However, in the case of a USB device driver, 
>> it is currently required as the USB framework is not MPSAFE, so requires 
>> Giant.
> Thanks for clarification. Does it mean that I can ignore this notice when 
> dealing with USB framework ?

For now, yes.  When, at some point, the USB framework is MPSAFE, we'll need to 
remove IFF_NEEDSGIANT, and I'd make sure that your device driver is as ready 
as it can be to operate Giant-free once that's done.

Robert N M Watson
Computer Laboratory
University of Cambridge

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