[Xen-bugs] [Bug 366] kernel BUG at arch/xen/kernel/smpboot.c:186 (vcpu_prepare)!

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=366





------- Additional Comments From grimm@xxxxxxxxxx  2005-11-14 16:50 -------
Created an attachment (id=101)
 --> (http://bugzilla.xensource.com/bugzilla/attachment.cgi?id=101&action=view)
debugging statements in set_gdt and get_page_type

Putting some debugging statements (the attached patch), i think i tracked the
problem down to set_gdt failing.  More specifically, get_page_type fails
(set_gdt calls get_page_and_type, which then calls get_page_type).   

The path of execution seems to hit the failure case because x & PGT_count_mask
!= 0.  Could the page retrieved by get_page in get_page_and_type already have a
reference count?

Enabling fast FPU save and restore... done.
Enabling unmasked SIMD FPU exception support... done.
Checking 'hlt' instruction... disabled
(XEN) Enter set_gdt for vcpuid:1
(XEN) About to call get_page_and_type for frame 0
(XEN) Enter set_gdt for vcpuid:2
(XEN) About to call get_page_and_type for frame 0
(XEN) Enter set_gdt for vcpuid:3
(XEN) About to call get_page_and_type for frame 0
(XEN) vcpuid: 0
(XEN) x: f0000001
(XEN) type: a0000000
(XEN) x & PGT_type_mask: e0000000
(XEN) x & PGT_count_mask: 1
(XEN) type & PGT_type_mask: a0000000
(XEN) Bad type in get_page_type
(XEN) failed in set_gdt for vcpuid:3
kernel BUG at arch/xen/kernel/smpboot.c:192 (vcpu_prepare)!
 [<c010772a>] vcpu_prepare+0x1ea/0x200
 [<c01074d0>] cpu_bringup+0x0/0x70
 [<c010a0d8>] divide_error+0x0/0x8
 [<c010a218>] debug+0x0/0x11
 [<c010a25c>] int3+0x0/0x24
 [<c010a280>] overflow+0x0/0xc
 [<c010a28c>] bounds+0x0/0xc
 [<c010a298>] invalid_op+0x0/0xc
 [<c010a1f8>] device_not_available+0x0/0x20
 [<c010a2a4>] coprocessor_segment_overrun+0x0/0xc
 [<c010a2b0>] invalid_TSS+0x0/0xc
 [<c010a2bc>] segment_not_present+0x0/0xc
 [<c010a2c8>] stack_segment+0x0/0xc
 [<c010a2d4>] general_protection+0x0/0xc
 [<c010a2ec>] page_fault+0x0/0xc
 [<c010a2f8>] fixup_4gb_segment+0x0/0x18
 [<c010a1e0>] coprocessor_error+0x0/0xc
 [<c010a2e0>] alignment_check+0x0/0xc
 [<c010a1ec>] simd_coprocessor_error+0x0/0xc
 [<c0109f1c>] system_call+0x0/0x32
 [<c010a110>] hypervisor_callback+0x0/0x34
 [<c010a1bc>] failsafe_callback+0x0/0x24
 [<c05937e6>] smp_prepare_cpus+0x166/0x260
 [<c01040b8>] init+0x38/0x1b0
 [<c0104080>] init+0x0/0x1b0
 [<c0107c1d>] kernel_thread_helper+0x5/0x18
Kernel panic - not syncing: BUG!
 smp_send_stop disable_local_APIC


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