ARM: SMP: BUG with PREEMPT enabled

[Shilimkar, Santosh]

Russell,

On the latest ARM kernel(v2.6.32-rc4),I have observed a BUG() dump when PREEMPT is enabled.
Attached is the detailed log for your reference.

<snip>
**********************************************************
BUG: using smp_processor_id() in preemptible [00000000] code: init/1
caller is flush_tlb_mm+0x44/0x70
Backtrace: 
[<c00225c4>] (dump_backtrace+0x0/0x110) from [<c01713a0>] (dump_stack+0x18/0x1c)
 r7:00000000 r6:c00234f0 r5:00000001 r4:c7828000
[<c0171388>] (dump_stack+0x0/0x1c) from [<c0135364>] (debug_smp_processor_id+0xc0/0xf0)
[<c01352a4>] (debug_smp_processor_id+0x0/0xf0) from [<c00234f0>] (flush_tlb_mm+0x44/0x70)
 r7:00000000 r6:c60b41a0 r5:c60b4154 r4:00000001
[<c00234ac>] (flush_tlb_mm+0x0/0x70) from [<c0039568>] (dup_mm+0x304/0x38c)
 r5:c1f09058 r4:00000000
[<c0039264>] (dup_mm+0x0/0x38c) from [<c0039de4>] (copy_process+0x7b8/0xeb0)
[<c003962c>] (copy_process+0x0/0xeb0) from [<c003a638>] (do_fork+0x15c/0x29c)
[<c003a4dc>] (do_fork+0x0/0x29c) from [<c0021df0>] (sys_clone+0x34/0x3c)
[<c0021dbc>] (sys_clone+0x0/0x3c) from [<c001efa0>] (ret_fast_syscall+0x0/0x2c)
**************************************************************

As evident from the log " smp_processor_id " is used in preemptible code. This gets triggered from 
flush_tlb_mm() -->
	local_flush_tlb_mm()
	{
		if (cpu_isset(smp_processor_id(), vma->vm_mm->cpu_vm_mask)) ^^
	}

This can be guuarded using "get_cpu/put_cpu" pair which can make it preemption safe but I am not sure whether that is the right fix.

Let me know your remarks !!

Regards,
Santosh

-------------- next part --------------
A non-text attachment was scrubbed...
Name: preempt.log
Type: application/octet-stream
Size: 9633 bytes
Desc: preempt.log
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20091013/cb570ae4/attachment.obj>