Date: Thu, 16 Apr 2009 15:53:35 -0600 From: Scott Long <scottl@samsco.org> To: John Baldwin <jhb@freebsd.org> Cc: Damian Gerow <dgerow@afflictions.org>, freebsd-current@freebsd.org, Richard Todd <rmtodd@ichotolot.servalan.com> Subject: Re: ZFS checksum errors on umass(4) insertion Message-ID: <49E7A8DF.9080902@samsco.org> In-Reply-To: <200904161748.08402.jhb@freebsd.org> References: <49BD117B.2080706@163.com> <200904161624.51920.jhb@freebsd.org> <49E7A404.5090208@samsco.org> <200904161748.08402.jhb@freebsd.org>
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John Baldwin wrote: > On Thursday 16 April 2009 5:32:52 pm Scott Long wrote: >> John Baldwin wrote: >>> Can you please try http://www.FreeBSD.org/~jhb/patches/dma_pg.patch? This >>> lines up with your analysis in that it fixes a problem in the bounce > buffer >>> code that was introduced with the new USB stack (and only triggers when > the >>> USB code has to use a bounce buffer). >>> >> As a data point, most normal I/O is not going to trigger this bug, even >> if it gets bounced. I/O using O_DIRECT can, and GEOM discovery I/O can >> as well. Since memory is allocated from the top of the system, I think >> that the damage gets done early during boot, and then propagates out >> over time as the system becomes busier. > > Hmm, are you sure regular I/O won't trigger it as well? All it takes is for > any USB transfer that starts off within a page to get a page into a non-zero > offset and later have a request >= PAGE_SIZE bounce. Since the VM is going > to always ask for I/O to pages (e.g. GET/PUTPAGES) normal disk I/O would > break if it uses the bad bounce page I think. > Sorry, I knew what I meant but didn't say it that well. Once it gets triggered, it poisons that bounce page from thereon out, and any I/O will be affected. But the only I/O that will typically trigger it is GEOM scanning and O_DIRECT. Scott
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