Date: Tue, 17 Dec 2013 14:34:01 -0500 From: John Baldwin <jhb@freebsd.org> To: Mateusz Guzik <mjguzik@gmail.com> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Mateusz Guzik <mjg@freebsd.org> Subject: Re: svn commit: r259407 - head/sys/kern Message-ID: <201312171434.01345.jhb@freebsd.org> In-Reply-To: <20131217181745.GB7535@dft-labs.eu> References: <201312150411.rBF4Bhtg018852@svn.freebsd.org> <201312171141.49251.jhb@freebsd.org> <20131217181745.GB7535@dft-labs.eu>
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On Tuesday, December 17, 2013 1:17:45 pm Mateusz Guzik wrote: > On Tue, Dec 17, 2013 at 11:41:49AM -0500, John Baldwin wrote: > > On Saturday, December 14, 2013 11:11:43 pm Mateusz Guzik wrote: > > > Author: mjg > > > Date: Sun Dec 15 04:11:43 2013 > > > New Revision: 259407 > > > URL: http://svnweb.freebsd.org/changeset/base/259407 > > > > > > Log: > > > proc exit: don't take PROC_LOCK while freeing rlimits > > > > > > Code wishing to check rlimits of some process should check whether it > > > is exiting first, which current consumers do. > > > > Does this measurably reduce contention? > > > > No, this is just a cosmetic change I did while doing some other work > with rlimits. > > It would use some more cosmetic work (e.g. no reason not to > lim_free(p->plimit); p->p_limit = NULL) and maybe I'll get to that > later unless this kind of stuff is unwanted. I find it useful to leave the locking in place so it is clear that p_limit is always written to with the lock held. If we ever got a static analyzer that understood locking rules then leaving this locking in would reduce false positives. When I first did locking for fields in struct proc I did it by hand based on grepping the source tree for all uses of a field and ensuring they were locked. I think it might be more confusing later on for another reader to see unlocked access and then have to think about why that is safe. -- John Baldwin
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