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Re: struct ifnet and ifaddr handling [was: Re: Making global variables of if.c MPSAFE]
Date: 2014年11月13日 12:43:26 +0900
From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
Here is a new patch: http://www.netbsd.org/~ozaki-r/psz-ifnet.diff
I think the patch reflects rmind's suggestions:
- Use pserialize for IFNET_FOREACH
- but use a lock for blockable/sleepable critical sections
- cpu_intr_p workaround for HW interrupt
Any comments?
Hmm...some quick notes from a non-expert in sys/net:
- You call malloc(M_WAITOK) while the ifnet lock is held, in
if_alloc_sadl_locked, which is not allowed.
- You call copyout in a pserialize read section, in ifconf, which is
not allowed because copyout may block.
- I don't know what cpu_intr_p is working around but it's probably not
a good idea!
Generally, all that you are allowed to do in a pserialize read section
is read a small piece of information, or grab a reference to a data
structure which you are then going to use outside the read section.
I don't think it's going to be easy to scalably parallelize this code
without restructuring it, unless as a stop-gap you use a heaver-weight
reader-writer lock like the prwlock at
<https://www.NetBSD.org/~riastradh/tmp/20140517/rwlock/prwlock.c>.
(No idea how much overhead this might add.)
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