Date: Thu, 19 Dec 2013 16:40:42 +0100 From: Julian Elischer <julian@elischer.org> To: John Baldwin <jhb@freebsd.org>, 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: <52B3137A.4000805@elischer.org> In-Reply-To: <201312171434.01345.jhb@freebsd.org> References: <201312150411.rBF4Bhtg018852@svn.freebsd.org> <201312171141.49251.jhb@freebsd.org> <20131217181745.GB7535@dft-labs.eu> <201312171434.01345.jhb@freebsd.org>
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On 12/17/13, 8:34 PM, John Baldwin wrote: > 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. > leave the locks there but commented out with an explanatory comment.
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