Re: [PATCH] Xen: Fix pte unpin BUG when !CONFIG_SMP

[Alex Nixon]

Jeremy Fitzhardinge wrote:
> Alex Nixon wrote:
>   
> > We still need to pin PTEs, even if there are no PTE locks.  Otherwise we'll BUG whenever there aren't PTE locks (i.e. whenever NR_CPUS < CONFIG_SPLIT_PTLOCK_CPUS), as we try to unpin PTEs which were never pinned in the first place.
> >   
> >     
>
> Where does the unpin happen?  xen_unpin_page() also checks to see if it
> took the lock before trying to unpin, symmetric with xen_pin_page().
>
>     J
>   
Here's the backtrace of the BUG() the patch addresses.  Now you've 
pointed it out - I see the asymmetry - and also suspect some ptes are 
being left pinned.

I'm having trouble finding a cleaner solution which solves this but 
doesn't incite more BUGs. 

Perhaps you have an idea?

- Alex


------------[ cut here ]------------
kernel BUG at 
/local/scratch/hotplug.linux.trees.git/arch/x86/xen/enlighten.c:847!
invalid opcode: 0000 [#1]
Modules linked in:

Pid: 1, comm: init Tainted: G        W (2.6.27-rc5-tip #352)
EIP: 0061:[<c10038fe>] EFLAGS: 00010282 CPU: 0
EIP is at pin_pagetable_pfn+0x3f/0x4b
EAX: ffffffea EBX: df82bd7c ECX: 00000001 EDX: 00000000
ESI: 00007ff0 EDI: c1a579e0 EBP: df82bd94 ESP: df82bd7c
DS: 007b ES: 007b FS: 0000 GS: 0000 SS: e021
Process init (pid: 1, ti=df82a000 task=df82c000 task.ti=df82a000)
Stack: 00000004 0014a0a1 00000000 0001fb4f c1a579e0 c1a579e0 df82bda4 
c1003dd3
      003f69e0 c157e024 df82bdac c1003e0e df82bdc8 c101b577 00000000 
00000000
      003f69e0 c1661000 dfb4e000 df82be28 c1062d35 1fb4f067 00000000 
dfb4e000
Call Trace:
[<c1003dd3>] ? xen_release_ptpage+0x61/0x80
[<c1003e0e>] ? xen_release_pte+0xd/0xf
[<c101b577>] ? __pte_free_tlb+0x46/0x5f
[<c1062d35>] ? free_pgd_range+0x1dc/0x391
[<c10794e5>] ? setup_arg_pages+0x1b8/0x22b
[<c109b3cb>] ? load_elf_binary+0x3f1/0x10c6
[<c1062206>] ? get_user_pages+0x316/0x394
[<c1078bef>] ? get_arg_page+0x2c/0x7e
[<c1078bc1>] ? put_arg_page+0x8/0xa
[<c1078d97>] ? copy_strings+0x156/0x160
[<c1078e51>] ? search_binary_handler+0x7b/0x1c0
[<c1079e20>] ? do_execve+0x13a/0x1c4
[<c1007164>] ? sys_execve+0x29/0x4b
[<c1008a2e>] ? syscall_call+0x7/0xb
[<c100b11f>] ? kernel_execve+0x17/0x1c
[<c1003140>] ? run_init_process+0x17/0x19
[<c10031e8>] ? init_post+0xa6/0xf6
[<c100965f>] ? kernel_thread_helper+0x7/0x10
=======================

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