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SubjectRe: [PATCH 2.6.11-rc3 01/11] ide: task_end_request() fix
 Hello, Bartlomiej.

On Tue, Mar 01, 2005 at 03:30:32PM +0100, Bartlomiej Zolnierkiewicz wrote:
> On Sun, 27 Feb 2005 15:49:22 +0900, Tejun Heo <htejun@gmail.com> wrote:
> >
> > Taskfile DMA path is still broken. Also calling ide_end_request()
> > will work there, but IMHO it's just cleaner to finish special commands
> > inside ide_end_drive_cmd(). Currently,
>
> I agree but please note that your patch makes *all* taskfile registers to
> be exposed through HDIO_DRIVE_TASKFILE regardless of ->rf_in_flags
> (and obviously later you can't revert this change).
>
> > * Successful flagged taskfile -> ide_end_drive_cmd()
> > * All other successful non-DMA special cmds -> ide_end_request()
> > * Successful DMA taskfile -> segfault
>
> Have you tested it? Why would it segfault?
>

It's the same reason why PIO taskfiles were broken. rq->rq_disk is
NULL for taskfile requests.

ide_startstop_t ide_dma_intr (ide_drive_t *drive)
{
...
printk("**HERE0***\n");
drv = *(ide_driver_t **)rq->rq_disk->private_data;;
printk("**HERE1***\n");
drv->end_request(drive, 1, rq->nr_sectors);
return ide_stopped;
...
}
And, my test program does the following TASKFILE ioctl.

memset(&task, 0, sizeof(task));
task.req.out_size = sizeof(task.outbuf);
task.req.in_size = sizeof(task.inbuf);

task.req.io_ports[2] = 1; /* nsector */
task.req.io_ports[3] = sector; /* LBA [7:0] */
task.req.io_ports[4] = sector >> 8; /* LBA [15:8] */
task.req.io_ports[5] = sector >> 16; /* LBA [23:16] */
task.req.io_ports[6] = 0x40 | ((sector >> 24) & 0xf); /* select */
task.req.io_ports[7] = WIN_READDMA; /* command */
task.req.req_cmd = IDE_DRIVE_TASK_IN;
task.req.data_phase = TASKFILE_IN_DMA;
Then, the kernel oopses...

**HERE0***
Unable to handle kernel NULL pointer dereference at virtual address 00000038
printing eip:
c026bce4
*pde = 00000000
Oops: 0000 [#1]
PREEMPT SMP
Modules linked in: nfs lockd sunrpc e1000 eepro100 e100 mii floppy
CPU: 0
EIP: 0060:[<c026bce4>] Not tainted VLI
EFLAGS: 00010082 (2.6.11-rc3-work-i386)
EIP is at ide_dma_intr+0x84/0xd0
eax: 00000000 ebx: f5e79d6c ecx: c03a678c edx: 00000001
esi: c048b3b0 edi: c048b3b0 ebp: c0435efc esp: c0435ee0
ds: 007b es: 007b ss: 0068

> > * All failed special cmds -> ide_end_drive_cmd()
> >
> > It just shouldn't be like this. :-(
>
> Yep.
>
> > >
> > > > * enables TASKFILE ioctls to get valid register outputs on
> > > > successful completion.
> > >
> > > This change makes *all* taskfile registers to be read on completion
> > > of *any* command. Currently this is done only for flagged taskfiles
> > > and commands using no-data protocol.
> > >
> > > With all your changes it will be also done for:
> > > * HDIO_DRIVE_[TASKFILE,CMD] ioctls
> > > * /proc/ide/hd?/{identify,smart_thresholds,smart_values}
> > > but reading back all registers is not always needed.
> >
> > None is on a hot path or even near to one, but maybe I don't have
> > enough experience with old hardware. Are there some old hardware
> > which make the additional reads stand out?
>
> I dunno, better be safe then sorry, after all we are working
> on the *stable* kernel tree.
>
> Converting HDIO_DRIVE_CMD and in-kernel users to
> soon-to-be-implemented ;-) sane discrete interface shouldn't
> require much effort.
>
> > > It is already bad enough (and we can't fix it cause it is exported
> > > to user-space through HDIO_DRIVE_TASKFILE), we shouldn't
> > > make it worse.
> >
> > Yeah, the whole IDE ioctl interface seems disturbingly messy. :-(
> >
> > * Register output is available only if
> > 1. The command fails.
> > 2. The command is a flagged taskfile.
>
> 3. the command uses no-data protocol
>

Yes, that one. :-)

> > * taskfile->device_head is used regardless of outflags setting.
> > * In flagged taskfile, taskfile->device_head can turn on the device
> > bit, so we can issue commands to hdb with permissions to hda.
> > * In TASK and TASKFILE, LBA commands can be issued to drives in CHS
> > mode but the reverse isn't true. However, in TASKFILE, if the
> > command isn't flagged, the lower nibble of device register is
> > zeroed depending on addressing setting.
> > * taskfile->data endianess is reversed on big endian machines.
> > * ide_reg_valid_t endianess issue.
> > * And, none of above is documented.
> >
> > So, I don't know. Do you think we should keep all of the above
> > behaviors? Please let me know; then, I'll update ioctl/hdio.txt so
>
> Now read again the list above and think about amount of time required
> to *safely* fix all the issues mentioned vs introducing sane interface.
> Please also note that once we expose something to user-space
> applications may depend on the broken behavior so we can't fix all
> issues anyway.

So, I guess we're keeping most of them.

> If somebody implements SG_IO ioctl and SCSI command pass-through
> from libata for IDE driver (and add possibility for discrete taskfiles), we can
> just deprecate HDIO_DRIVE_TASKFILE, forget about it and some time later
> remove this FPOS.

That sounds sweet.

> > that people can at least know these gotchas.
>
> Please do so, thanks.

Yes, I'll do.

Thanks.

--
tejun

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