Date: Sun, 1 Aug 2004 20:15:45 -0400 From: Brian Fundakowski Feldman <green@freebsd.org> To: Nate Lawson <nate@cryptography.com> Cc: sos@deepcore.dk Subject: Re: memory corruption/panic solved ("FAILURE - ATAPI_IDENTIFY no interrupt") Message-ID: <20040802001545.GA91621@green.homeunix.org> In-Reply-To: <410D853F.6080704@cryptography.com> References: <410AD054.8070202@root.org> <20040731064433.GD33220@green.homeunix.org> <410D853F.6080704@cryptography.com>
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On Sun, Aug 01, 2004 at 05:05:19PM -0700, Nate Lawson wrote: > Brian Fundakowski Feldman wrote: > >On Fri, Jul 30, 2004 at 03:48:52PM -0700, Nate Lawson wrote: > >>I've tracked down the source of the memory corruption in -current that > >>results when booting with various CD and DVD drives (especially the ones > >>that come with Thinkpads including T23, R32, T41, etc.) The panic is > >>obvious when running with INVARIANTS ("memory modified after free") but > >>not so obvious in other configurations. For instance, without > >>INVARIANTS, part of the rt_info structure is corrupted on my wireless > >>card, resulting in a panic during ifconfig on boot. This is likely the > >>source of other problems, including phk's ACPI panic (again, only > >>triggered when booting with the CD drive in the bay.) > >> > >>The root problem is that ata_timeout() fires and calls ata_pio_read() > >>which overwrites 512 bytes random memory. There are actually two bugs > >>here that overwrite memory. The code path is as follows: > > > >Good job identifying it more exactly. I decided it should just > >fundamentally > >be using GEOM primitives everywhere to move the solutions to all these > >side cases into where they're already handled generically... still think > >that's probably the right solution, but I'm glad to see this specific > >problem fixed. > > I'm not sure if this is a troll or not but I'll answer it seriously. > GEOM and other upper layers are never the right place to handle error > recovery for transactions initiated at the lower layers (like this > device scan). > > In every system I've seen, error recovery is the hardest part of storage > code to get right and is seldom well-tested. It's a very difficult > problem that involves a lot of careful fault injection/testing. > Divergence in hardware fault handling behavior only complicates things. What would make it a troll? If GEOM were used so that all transactions were centrallized, and there were one timeout mechanism used to run the request queues for ATA, it wouldn't be racing and crashing when a device reset occurs (and it would be a net reduction in code). -- Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\ <> green@FreeBSD.org \ The Power to Serve! \ Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\
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