Remaining non-MPSAFE netisr handlers

Robert Watson rwatson at
Fri Jul 4 00:30:19 UTC 2008

On Mon, 26 May 2008, Robert Watson wrote:

> In the continuing campaign to eliminate the Giant lock from the dregs of the 
> network stack, I thought I'd send out a list of non-MPSAFE netisr handlers:
> Location			Handler		Removed with IFF_NEEDSGIANT
> dev/usb/usb_ethersubr.c:120	usbintr		Yes
> net/if_ppp.c:277		pppintr		Yes
> netinet6/ip6_input.c		ip6_input	No
> The plan for 8.0 is to remove the NETISR_MPSAFE flag -- all netisr handlers 
> will be executed without the Giant lock.  This doesn't prohibit acquiring 
> Giant in the handler if required, although that's undesirable for the 
> obvious reasons (potentially stalling interrupt handling, etc).  Obviously, 
> what would be most desirable is eliminating the remaining requirement for 
> Giant in the IPv6 input path, primarily consisting of mld6 and nd6.
> With this in mind, my current plan is to remove the flag and add explicit 
> Giant acquisition for any remaining handlers in June when IFF_NEEDSGIANT 
> device drivers are disabled.

I've now removed the NETISR_MPSAFE flag -- all netisr handlers are now assumed 
to DTRT with respect to locking.  At least until usb and ppp are sorted out, 
I've introduced NETISR_FORCEQUEUE as an interim measure, which allows 
protocols to request that they always operate the deferred dispatch, meaning 
they can acquire Giant if they need to, and modified those two to do so. 
That should go away by 8.0 also.

Robert N M Watson
Computer Laboratory
University of Cambridge

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