Date: Thu, 18 Jul 2013 11:40:51 -0700 From: George Hartzell <hartzell@alerce.com> To: Richard Todd <rmtodd@servalan.servalan.com> Cc: freebsd-stable@freebsd.org, hartzell@alerce.com Subject: Re: Help with filing a [maybe] ZFS/mmap bug. Message-ID: <20968.14003.813473.517439@gargle.gargle.HOWL> In-Reply-To: <x7vc48sb5e.fsf@ichotolot.servalan.com> References: <20967.760.95825.310085@gargle.gargle.HOWL> <x7vc48sb5e.fsf@ichotolot.servalan.com>
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Richard Todd writes: > George Hartzell <hartzell@alerce.com> writes: > > > Hi All, > > > > I have what I think is a ZFS related bug. > > [...] > > [summary: Picard seems to trigger an mmap consistency bug in ZFS]. > > [...] > Anyway, what I'd suggest is the following: see if my patch for py-mutagen > disabling the mmap() in those two functions lets you run picard reliably. Removing the mmap support from those two routines seems to avoid the issue. > If so, then the issue is triggered by one or both of those two routines; > hack them to print out the exact offsets used on each call and use that to > try and code up a simple C++ test case. > [...] Your test case doesn't use mmap, I assume that you've offered it up as a hint, not as something that's nearly done. The shell script in particular seems useful. In my case I'd want to find a particular set of file size, offset, and insertion size that triggers the problem and code up a c/c++ equiv. of the mmap calls that py-mutagen does. Right? I'm hesistant about that. I believe (and will try to prove) that the problem does not occur deterministically for a particular track between different test runs. I'm worried that it's not as simple as "using mmap to insert 27 bytes into a 1024 bytes file at pos 42 causes corruption" but rather that it depends on a more complex set of interactions. My next step will be to see if a track that has trouble in one run has trouble in another. If not, then I'm not sure that a simple test will be successful. g.
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