On Wed, May 11, 2005 at 01:42:35PM -0700, Paul Jackson wrote:
> So what we'd really like to do would be to first fallback to all the
> cpus allowed in the specified tasks cpuset (no walking the cpuset
> hierarchy), and see if any of those cpus are still online to receive
> this orphan task.  Unless someone has botched the system configuration,
> and taken offline all the cpus in a cpuset, this should yield up a cpu
> that is still both allowed and online.  If that fails, then to heck with
> honoring cpuset placement - just take the first online cpu we can find.
> 

I tried your suggestion, but hit another oops. This has more to do with
hotplug+preempt looks like

Code: fc 89 ec 5d e9 8b 0e 00 00 c7 04 24 5c 49 41 c0 e8 7f 39 00 00 e8 da 87 fe ff eb c1 0f 0b 36 11 32 96 41 c0 eb 92 83 f8
 <6>note: cpuoff.sh[25439] exited with preempt_count 1
scheduling while atomic: cpuoff.sh/0x10000001/25439
 [<c04010d2>] schedule+0x4b2/0x4c0
 [<c0152da0>] unmap_page_range+0xc0/0xe0
 [<c0401988>] cond_resched+0x28/0x40
 [<c0152f56>] unmap_vmas+0x196/0x290
 [<c0157c93>] exit_mmap+0xa3/0x1a0
 [<c011ce53>] mmput+0x43/0x100
 [<c01222f0>] do_exit+0xf0/0x3b0
 [<c01047da>] die+0x18a/0x190
 [<c0104bb0>] do_invalid_op+0x0/0xd0
 [<c0104c5e>] do_invalid_op+0xae/0xd0
 [<c011bbe7>] migrate_dead+0xa7/0xc0
 [<c0400f14>] schedule+0x2f4/0x4c0
 [<c040112b>] preempt_schedule+0x4b/0x70
 [<c040112b>] preempt_schedule+0x4b/0x70
 [<c0103fd7>] error_code+0x4f/0x54
 [<c040007b>] svc_proc_unregister+0x1b/0x20
 [<c011007b>] __acpi_map_table+0x7b/0xc0
 [<c011bbe7>] migrate_dead+0xa7/0xc0
 [<c011fef9>] profile_handoff_task+0x39/0x50
 [<c011bc62>] migrate_dead_tasks+0x62/0x90
 [<c011bda6>] migration_call+0x116/0x2c0
 [<c0142102>] __stop_machine_run+0x92/0xb0
 [<c012ddad>] notifier_call_chain+0x2d/0x50
 [<c013a3cb>] cpu_down+0x16b/0x2a0
 [<c027db0b>] store_online+0x5b/0x80
 [<c027ab25>] sysdev_store+0x35/0x40
 [<c019f14e>] flush_write_buffer+0x3e/0x50
 [<c019f1b8>] sysfs_write_file+0x58/0x80
 [<c0163a36>] vfs_write+0xc6/0x180
 [<c0163bc1>] sys_write+0x51/0x80
 [<c01034e5>] syscall_call+0x7/0xb


On 2.6.12-rc4-mm1 it is even worse, it panics

Booting processor 2/1 eip 3000
Calibrating delay using timer specific routine.. 1800.08 BogoMIPS (lpj=900043)
CPU2: Intel Pentium III (Cascades) stepping 04
Unable to handle kernel NULL pointer dereference<7>CPU0 attaching sched-domain:
 at virtual address 00000001
 printing eip:
00000001
*pde = 000001e3
*pte = 00000001
Oops: 0000 [#1]
PREEMPT SMP
Modules linked in:
CPU:    2
EIP:    0060:[<00000001>]    Not tainted VLI
EFLAGS: 00010006   (2.6.12-rc4-mm1)
EIP is at 0x1
eax: c18c0000   ebx: c04758a0   ecx: 00000001   edx: e8c13eb4
esi: ffffffff   edi: c185c030   ebp: c18c1f80   esp: c18c1f2c
ds: 007b   es: 007b   ss: 0068
Process swapper (pid: 0, threadinfo=c18c0000 task=c185c030)
Stack: c0114e0d e8c13eb4 c18c0000 c0103ecc c18c0000 00000008 00000002 ffffffff
       c185c030 c18c1f80 00000001 0000007b 0000007b fffffffb c04048a0 00000060
       00000206 c040511c 00000003 00000000 00000000 c18c0000 c01033ee 00000003
Call Trace:
 [<c0114e0d>] smp_call_function_interrupt+0x3d/0x60
 [<c0103ecc>] call_function_interrupt+0x1c/0x24
 [<c04048a0>] schedule+0x0/0x7c0
 [<c040511c>] preempt_schedule_irq+0x4c/0x80
 [<c01033ee>] need_resched+0x1f/0x21
 [<c011516f>] start_secondary+0x10f/0x1a0
Code:  Bad EIP value.
 <0>Kernel panic - not syncing: Fatal exception in interrupt
Booting processor 3/2 eip 3000
Initializing CPU#3

I really havent had a chance to investigate whats going on, should be able to
do that tomorrow. Here is the patch I tried, my .config and scripts

	-Dinakar