Date: Wed, 8 Oct 2003 11:12:51 +0100 From: Bruce M Simpson <bms@spc.org> To: Harti Brandt <brandt@fokus.fraunhofer.de> Cc: freebsd-hackers@freebsd.org Subject: Re: Dynamic reads without locking. Message-ID: <20031008101251.GG6524@saboteur.dek.spc.org> In-Reply-To: <20031008114506.I63940@beagle.fokus.fraunhofer.de> References: <20031008083059.GA520@garage.freebsd.pl> <20031008114506.I63940@beagle.fokus.fraunhofer.de>
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On Wed, Oct 08, 2003 at 11:51:06AM +0200, Harti Brandt wrote: > You need to lock when reading if you insist on consistent data. Even a > simple read may be non-atomic (this should be the case for 64bit > operations on all our platforms). Or keep a generation count to detect pre-emption (the devstat code does this, amongst other things), and try again if you lost the race. Or insist on atomic reads, which must complete and must not be pre-empted by definition (although the SMP case is/can be different!). BMS
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