On Tue, Feb 06, 2007 at 10:29:54AM -0000, Martyn Welch wrote:
> I need to allocate a large buffer for DMA transfers in a driver I'm
> working on. I understand that the kernel normally will not allocate
> coherent buffers larger than 128KB, the suggested solution (from
> O'Reilly's ldd3) seems to be to compile the driver into the kernel and
> allocate a buffer at boot using alloc_bootmem_low(). When I tried this I
> get a kernel panic:
Are you trying to do this from a module? That would explain it doesn't
work.
> ========================================================================
> =========
>
> BUG: unable to handle kernel NULL pointer dereference at virtual address
> 000002f0
> printing eip:
> c021ca95
> *pde = 00000000
> Oops: 0000 [#1]
> SMP
> Modules linked in:
> CPU: 0
> EIP: 0060:[<c021ca95>] Not tainted VLI
> EFLAGS: 00010202 (2.6.17.9 #23)
> EIP is at find_next_zero_bit+0x35/0xb0
> eax: 000000bc ebx: c0522c20 ecx: 00000013 edx: ffffffff
> esi: 00000000 edi: 000002f0 ebp: 00038000 esp: c17ffef8
> ds: 007b es: 007b ss: 0068
> Process swapper (pid: 1, threadinfo=c17fe000 task=dfbdfa10)
> Stack: 00000000 c0522c20 00000000 01000000 00038000 c04e2894 00000000
> 00038000
> 00001793 00000000 ffffffff 00000000 ffffff80 00000246 00000013
> 00000001
> 00001793 00000000 00000001 c0522c20 01000000 00000080 00001000
> c04e2c84
> Call Trace:
> <c04e2894> __alloc_bootmem_core+0xe4/0x3a0 <c04e2c84>
> __alloc_bootmem_nopanic+0x64/0x80
> <c04e2cc0> __alloc_bootmem+0x20/0x50 <c04eb5cb>
> universeII_init+0x2b/0x40
> <c0100423> init+0x123/0x330 <c0102eea> ret_from_fork+0x6/0x14
> <c0100300> init+0x0/0x330 <c0100300> init+0x0/0x330
> <c0100e35> kernel_thread_helper+0x5/0x10
> Code: 20 89 74 24 08 8b 74 24 18 89 7c 24 0c c1 f8 05 83 e1 1f 89 6c 24
> 10 8d 3c 86 8b 6c 24 1c 89 5c 24 04 c7 04 24 00 00 00 00 74 22 <8b> 07
> c7 04 24 20 00 00 00 29 0c 24 d3 e8 f7 d0 0f bc c0 75 05
> EIP: [<c021ca95>] find_next_zero_bit+0x35/0xb0 SS:ESP 0068:c17ffef8
>
> ========================================================================
> =========
>
> The offending code:
>
> ========================================================================
> =========
>
> static int __init universeII_init(void)
> {
> void* buffer;
>
> printk(KERN_INFO "Loading driver.\n");
>
> buffer = alloc_bootmem(PAGE_SIZE);
>
> return 0;
> }
I hope you do understand you're leaking memory over here.
> ========================================================================
> =========
>
> I am using:
>
> kernel version 2.6.17.9
If you're not trying to allocate from a module, you might want to
update your kernel to 2.6.20 and see if you can recreate the Oops.
Erik
--
They're all fools. Don't worry. Darwin may be slow, but he'll
eventually get them. -- Matthew Lammers in alt.sysadmin.recovery
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