Messages in this thread | | | Date | Mon, 02 Nov 2009 14:16:44 +0100 | From | Eric Dumazet <> | Subject | Re: [net-next-2.6 PATCH RFC] TCPCT part 1d: generate Responder Cookie |
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William Allen Simpson a écrit : > Eric Dumazet wrote: >> cookie_hash() runs in a non preemptable context. CPU cannot change >> under us. >> >> (or else, we would not use __get_cpu_var(ipv4_cookie_scratch); ) >> >> And of course, each cpu gets its own scratch area, thanks to >> __get_cpu_var() >> > Interesting. I'm not sure that running CPU intensive functions like > SHA1 in > a non-preemptable context is a good idea. I'd assumed it wasn't! > > Perhaps you could point at the documentation in the code that explains > this?
I suggest you read Documentations/ files about softirq
http://docs.blackfin.uclinux.org/kernel/generated/kernel-hacking.xml
Large part of network code is run by softirq handler, and a softirq handler is not preemptable with another softirq (including itself).
> Perhaps a function header comment that mentions it?
So we are going to add a header to thousand of functions repeating this prereq ?
> > All I know is (from testing) that the tcp_minisockets.c caller is sometimes > called in a fashion that requires atomic allocation, and other times > does not!
Maybe callers have different contexts (running from softirq handler or from process context). Atomic ops are expensive and we try to avoid them if/when possible.
> > See my "Subject: query: tcpdump versus atomic?" thread from Oct 14th.
You probably add a bug in your kernel, leaving a function with unpaired lock/unlock of notallow_something/allow_something
There are books about linux internals that you could read if you want some extra documentation. Dont ask me details, I never read them :)
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