Re: kernel unaligned accesses on IA64 in IDE

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 21.08.2008 [16:54:26 -0500], Robin Holt wrote:
> > [   32.597792] outsl(496, e000000644678466, 3)
>                             ^^^^^^^^^^^^^^^^
> 
> This is expected to be an unsigned int * and typecast to that in outsl.
> Looks like the buffer being passed in is not properly aligned.  Time to
> go look at the caller.  Make sure buf is defined as an array of at least
> int size.  That should make this aligned on a 4 byte boundary instead of
> the 2 byte boundary it is on now.
> 
> You can cheat at finding the callers by putting
> 	WARN_ON(buf & 0x3);
> 	printk...

So I tried this and it gets quite hairy quickly (I think) because what's
unaligned is an IDE command buffer? There is a lot of pointer passing
and I get lost since I don't know the IDE/elevator code very well.

Here's the stack trace I'm looking at:

[    5.018347]  [<a000000100015420>] show_stack+0x80/0xa0
[    5.018348]                                 sp=e00000130307f930 bsp=e0000013030793b8
[    5.031782]  [<a000000100015470>] dump_stack+0x30/0x60
[    5.031783]                                 sp=e00000130307fb00 bsp=e0000013030793a0
[    5.045223]  [<a000000100094ff0>] warn_on_slowpath+0x90/0xe0
[    5.045225]                                 sp=e00000130307fb00 bsp=e000001303079378
[    5.059201]  [<a000000100517480>] ide_output_data+0x3c0/0x540
[    5.059204]                                 sp=e00000130307fbf0 bsp=e000001303079310
[    5.073248]  [<a0000001005309e0>] cdrom_transfer_packet_command+0x2c0/0x340
[    5.073249]                                 sp=e00000130307fbf0 bsp=e0000013030792d0
[    5.088519]  [<a000000100530ac0>] cdrom_do_newpc_cont+0x60/0x80
[    5.088522]                                 sp=e00000130307fc00 bsp=e0000013030792b0
[    5.102739]  [<a00000010052f1a0>] ide_cd_do_request+0x980/0x1420
[    5.102742]                                 sp=e00000130307fc00 bsp=e000001303079238
[    5.117064]  [<a00000010050fe00>] ide_do_request+0xca0/0x1d00
[    5.117066]                                 sp=e00000130307fc00 bsp=e0000013030791a0
[    5.131105]  [<a000000100511580>] do_ide_request+0x40/0x60
[    5.131107]                                 sp=e00000130307fc30 bsp=e000001303079180
[    5.144897]  [<a000000100384780>] elv_insert+0x280/0x5c0
[    5.144900]                                 sp=e00000130307fc30 bsp=e000001303079148
[    5.158507]  [<a000000100384c40>] __elv_add_request+0x180/0x240
[    5.158509]                                 sp=e00000130307fc30 bsp=e000001303079110
[    5.172733]  [<a000000100391730>] blk_execute_rq_nowait+0xd0/0x1e0
[    5.172734]                                 sp=e00000130307fc30 bsp=e0000013030790d0
[    5.187220]  [<a000000100391910>] blk_execute_rq+0xd0/0x240
[    5.187221]                                 sp=e00000130307fc30 bsp=e000001303079090
[    5.201091]  [<a000000100531f70>] ide_cd_queue_pc+0x130/0x2e0
[    5.201093]                                 sp=e00000130307fcc0 bsp=e000001303078fd0
[    5.215137]  [<a0000001005342f0>] ide_cdrom_packet+0x130/0x180
[    5.215139]                                 sp=e00000130307fd00 bsp=e000001303078f78
[    5.229281]  [<a000000100593080>] cdrom_mode_sense+0xc0/0xe0
[    5.229283]                                 sp=e00000130307fd10 bsp=e000001303078f40
[    5.243239]  [<a00000010052d9c0>] ide_cdrom_get_capabilities+0x80/0xc0
[    5.243240]                                 sp=e00000130307fd10 bsp=e000001303078f10
[    5.258084]  [<a000000100533890>] ide_cd_probe+0x810/0xf40
[    5.258086]                                 sp=e00000130307fd50 bsp=e000001303078e90
[    5.273709]  [<a00000010050a510>] generic_ide_probe+0x70/0xa0
[    5.273711]                                 sp=e00000130307fdc0 bsp=e000001303078e70
[    5.287774]  [<a0000001004bdaf0>] driver_probe_device+0x190/0x3a0
[    5.287775]                                 sp=e00000130307fdc0 bsp=e000001303078e28
[    5.302163]  [<a0000001004bdd80>] __driver_attach+0x80/0xe0
[    5.302164]                                 sp=e00000130307fdc0 bsp=e000001303078de8
[    5.316032]  [<a0000001004bc5a0>] bus_for_each_dev+0xc0/0x140
[    5.316034]                                 sp=e00000130307fdc0 bsp=e000001303078db0
[    5.330072]  [<a0000001004bd700>] driver_attach+0x40/0x60
[    5.330074]                                 sp=e00000130307fde0 bsp=e000001303078d90
[    5.343761]  [<a0000001004bd290>] bus_add_driver+0x370/0x4a0
[    5.343763]                                 sp=e00000130307fde0 bsp=e000001303078d48
[    5.357720]  [<a0000001004be3d0>] driver_register+0xd0/0x340
[    5.357721]                                 sp=e00000130307fde0 bsp=e000001303078d00
[    5.371693]  [<a0000001009a3ea0>] ide_cdrom_init+0x20/0x40
[    5.371695]                                 sp=e00000130307fde0 bsp=e000001303078ce8
[    5.385475]  [<a00000010000a5a0>] do_one_initcall+0x60/0x380
[    5.385477]                                 sp=e00000130307fde0 bsp=e000001303078ca8
[    5.399445]  [<a0000001009645b0>] kernel_init+0x370/0x420
[    5.399447]                                 sp=e00000130307fe20 bsp=e000001303078c68
[    5.413148]  [<a000000100013590>] kernel_thread_helper+0xd0/0x100
[    5.413149]                                 sp=e00000130307fe30 bsp=e000001303078c40
[    5.427547]  [<a00000010000a4c0>] start_kernel_thread+0x20/0x40
[    5.427548]                                 sp=e00000130307fe30 bsp=e000001303078c40

We are trying to send a sense command to the device and the buffer we
use (which is rq->cmd) is what is unaligned, I believe. I'm not sure how
useful I can be going forward...

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@us.ibm.com>
IBM Linux Technology Center