Date: Mon, 24 Sep 2001 14:13:37 -0700 (PDT) From: Matt Dillon <dillon@earth.backplane.com> To: Ian Dowse <iedowse@maths.tcd.ie> Cc: hackers@freebsd.org Subject: Re: VM Corruption - stumped, anyone have any ideas? Message-ID: <200109242113.f8OLDbV96558@earth.backplane.com> References: <200109242144.aa79348@salmon.maths.tcd.ie>
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:In message <200109241914.f8OJE4l95477@earth.backplane.com>, Matt Dillon writes:
:>
:>$8 = 58630
:>(kgdb) print vm_page_buckets[$8]
:
:What is vm_page_hash_mask? The chunk of memory you printed out below
:looks alright; it is consistent with vm_page_array == 0xc051c000. Is
:it just the vm_page_buckets[] pointer that is corrupt?
:
:The address 0xc08428cc is (char *)&vm_page_array[55060] + 28, and
:sizeof(struct vm_page) is 60, so 0xc08428cc is in the middle of
:a vm_page within vm_page_array[].
:
:Ian
(kgdb) print vm_page_buckets[58630]
$5 = (struct vm_page *) 0xc08428cc
(kgdb) print vm_page_array
$6 = 0xc051c000
(kgdb) print vm_page_hash_mask
$7 = 262143
(kgdb) print &vm_page_array[55060]
$11 = (struct vm_page *) 0xc08428b0
(kgdb) print &vm_page_array[55061]
$10 = (struct vm_page *) 0xc08428ec
Yowzer. How the hell did that happen! Yes, you're right, the
vm_page_array[] pointer has gotten corrupted. If we assume that
the vm_page_t is valid (0xc0842acc), then the vm_page_buckets[]
pointer should be that.
vm_page_buckets[58630] -> c08428cc
panic on vm_page_t m -> c0842acc
Ok, so the corruption here is that an 'a' turned into an '8'. 1010 turned
into 1000... a bit got cleared.
This is very similar to the corruption I found on one of Yahoo's
machines. Except on that machine two bits were changed. It's as though
some other subsystem is trying to manipulate a flag in a structure using
a bad structure pointer.
-Matt
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