[BUG] 2.6.25-rc1-git1 softlockup while bootup on powerpc

[Kamalesh Babulal]

Ingo Molnar wrote:
> * Kamalesh Babulal <kamalesh at linux.vnet.ibm.com> wrote:
> 
>> While booting with the 2.6.25-rc1-git1 kernel on the powerbox the 
>> softlockup is seen, with following trace.
> 
>> BUG: soft lockup - CPU#1 stuck for 61s! [insmod:377]
>> TASK = c00000077cb2f0e0[377] 'insmod' THREAD: c00000077cb28000 CPU: 1
>> NIP [c0000000001b172c] .radix_tree_gang_lookup+0xdc/0x1e4
>> LR [c0000000001a6f00] .call_for_each_cic+0x50/0x10c
>> Call Trace:
>> [c00000077cb2bb20] [c0000000001a6f60] .call_for_each_cic+0xb0/0x10c (unreliable)
>> [c00000077cb2bc60] [c00000000019ecd8] .exit_io_context+0xf0/0x110
>> [c00000077cb2bcf0] [c00000000006254c] .do_exit+0x820/0x850
>> [c00000077cb2bda0] [c000000000062648] .do_group_exit+0xcc/0xe8
>> [c00000077cb2be30] [c00000000000872c] syscall_exit+0x0/0x40
> 
> this call_for_each_cic/radix_tree_gang_lookup locked up, and all other 
> CPUs deadlocked in stopmachine, due to this one.
> 
> call_for_each_cic is in ./block/cfq-iosched.c uses RCU, but you've got 
> classic-RCU:
> 
>   CONFIG_CLASSIC_RCU=y
>   # CONFIG_PREEMPT_RCU is not set
> 
> so it's not related to the preempt-RCU changes either.
> 
> It is this part that locks up:
> 
>         do {
> ...
>                 nr = radix_tree_gang_lookup(&ioc->radix_root, (void **) cics,
>                                                 index, CIC_GANG_NR);
> ...
>         } while (nr == CIC_GANG_NR);
> ...
> 
> it seems the radix tree will yield new entries again and again. Either 
> it got corrupted, or some other CPU is filling it faster than we can 
> deplete it [unlikely i think].
> 
> 	Ingo

This softlockup is seen with the 2.6.25-rc1-git3 also. Let me know if you
need more details.

-- 
Thanks & Regards,
Kamalesh Babulal,
Linux Technology Center,
IBM, ISTL.