Date: Wed, 16 Apr 2008 14:27:37 -0700 From: Marcel Moolenaar <xcllnt@mac.com> To: Peter Grehan <grehan@freebsd.org> Cc: freebsd-ppc@freebsd.org Subject: Re: kernel stacks [eas: Re: G5 Bridge-mode MMU] Message-ID: <8D15A3AC-BEF7-46DF-9166-C1D44BFD32EE@mac.com> In-Reply-To: <9F6F2C83-79F1-4463-B9FF-4BBEB55B95B2@mac.com> References: <4804AE13.2060600@uchicago.edu> <4804C9E9.6010303@freebsd.org> <5CC81F06-7B59-4163-9AB8-2ACE4235A5AA@mac.com> <4804DD02.10304@freebsd.org> <058EEFE3-09D7-447A-93AB-3E90EC59ECDC@mac.com> <48053E46.4090700@freebsd.org> <E42FE735-C13E-44F8-A333-7F103E332C7E@mac.com> <48054DE6.10508@freebsd.org> <9F6F2C83-79F1-4463-B9FF-4BBEB55B95B2@mac.com>
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Follow-up... On Apr 15, 2008, at 10:54 PM, Marcel Moolenaar wrote: > > On Apr 15, 2008, at 5:52 PM, Peter Grehan wrote: >> Hi Marcel, >> >>>> Are you sure it isn't a genuine stack overflow ? >>> Positive. The panic happens after 4KB of stack has been used. >>>> You may be able to tell by bumping the size of tmpstk on a non- >>>> kstack0 boot and see how far up it's been used. >>> The backtrace also shows that. From inner-most to out-most >>> function in >>> the backtrace the stack pointers are roughly 4KB apart. >> >> Can you send the code snippet that you're using to set up the >> stack ? I can desk-check that, and then use it for my testing so we >> have the exact same setup. *snip* >> usb0: USB revision 1.0 > [thread pid 0 tid 100000 ] > Stopped at 0x3e9cc0: stwux r0, r1, r9, > db> bt > Tracing pid 0 tid 100000 td 0x4cb340 > 0xd00040f0: at usbd_transfer+0xb0 *snip* Found the problem: moea_rkva_alloc(). The first 4 pages of KVA are reserved for page zeroing and other special purpose uses. This was not accounted for in the original moea_bootstrap() code when the kernel stack was allocated, so the kernel stack overlapped with the pages returned by moea_rkva_alloc(). This is easily fixed... -- Marcel Moolenaar xcllnt@mac.com
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