linux-kernel - Re: [PATCH 00 of 31] x86: unification and xen updates

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Date:	Wed, 19 Mar 2008 15:15:33 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Ian Campbell <ijc@...lion.org.uk>
Subject: Re: [PATCH 00 of 31] x86: unification and xen updates

Ingo Molnar wrote:
> * Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>
>   
>>> config attached. randconfig generated, so it can have random 
>>> surprises enabled :)
>>>       
>> Thanks.  What was the workload?  Did it just happen, or were you doing 
>> something specific?
>>     
>
> simple bootup triggered it.
>   

Haven't managed to repro it yet, but DEBUG_PAGE_ALLOC turned up another 
case of doing tlb flushes with preempt on:

BUG: using smp_processor_id() in preemptible [00000000] code: init/1
caller is xen_flush_tlb+0xe/0xa2
Pid: 1, comm: init Not tainted 2.6.25-rc6-x86-latest.git #281
 [<c0234eed>] debug_smp_processor_id+0x99/0xb0
 [<c0103ca0>] xen_flush_tlb+0xe/0xa2
 [<c011d46b>] kernel_map_pages+0x104/0x125
 [<c0154f45>] get_page_from_freelist+0x32f/0x433
 [<c01444c4>] ? lock_acquire+0x90/0x9d
 [<c01550bd>] __alloc_pages+0x5e/0x2a5
 [<c015c5b3>] do_wp_page+0x2c9/0x653
 [<c017953f>] ? do_lookup+0x4f/0x146
 [<c0103e11>] ? xen_restore_fl+0x2e/0x52
 [<c01444c4>] ? lock_acquire+0x90/0x9d
 [<c015f720>] ? handle_mm_fault+0xa37/0xbb8
 [<c015f7a4>] handle_mm_fault+0xabb/0xbb8
 [<c0179332>] ? path_put+0x20/0x23
 [<c0103e11>] ? xen_restore_fl+0x2e/0x52
 [<c0103e11>] ? xen_restore_fl+0x2e/0x52
 [<c045699d>] ? do_page_fault+0x460/0x952
 [<c013b80d>] ? down_read_trylock+0x37/0x41
 [<c0456a51>] do_page_fault+0x514/0x952
 [<c0232116>] ? copy_to_user+0x2a/0x34
 [<c017e3ce>] ? sys_select+0x13e/0x164
 [<c045653d>] ? do_page_fault+0x0/0x952
 [<c0454eaa>] error_code+0x72/0x78


This code seems a bit fast and loose anyway, since it only does a local 
TLB flush, which means that other CPUs can still accessed free memory if 
they still have a stale TLB for it.  Having the tlb flush happen on a 
random CPU doesn't really affect things much.

    J
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