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SubjectRe: Kernel panic reading bad disk sector

Chris Ross escreveu:
> Russell King - ARM Linux escreveu:
>> On Wed, Nov 23, 2005 at 09:25:40AM +0000, Chris Ross wrote:
>>> Greg Ungerer escreveu:
>>>> Chris Ross wrote:
>>>>
>>>>> According System.map it is in the function ide_dma_timeout_retry.
>>>>
>>>> Ok, that is good information. I would try and figure out which
>>>> line of code in there is dereferencing a NULL pointer.
>>>
>>> It would seem to be this line
>>>
>>> rq->errors = 0;
>
> because rq is set to NULL by earlier the line
>
> ret = DRIVER(drive)->error(drive, "dma timeout retry",
> hwif->INB(IDE_STATUS_REG));

Which looks like the the correct thing to do. In idedisk_error once the
threshold for the maximum number of retries has been reached the request
is ended because it cannot be serviced

if (rq->errors >= ERROR_MAX)
DRIVER(drive)->end_request(drive, 0);

in idedisk_end_request the request is explicitly set to NULL because it
is now ended, in the code block...

if (!end_that_request_first(rq, uptodate, drive->name)) {
add_blkdev_randomness(MAJOR(rq->rq_dev));
blkdev_dequeue_request(rq);
HWGROUP(drive)->rq = NULL;
end_that_request_last(rq);
ret = 0;
}

Which means that ide_dma_timeout_retry should take account of the fact
that the request might no longer be valid before using it.

In other words it should be...

/* Check whether the request ended early due to disk errors */
if( rq ) {
rq->errors = 0;
rq->sector = rq->bh->b_rsector;
rq->current_nr_sectors = rq->bh->b_size >> 9;
rq->hard_cur_sectors = rq->current_nr_sectors;
rq->buffer = rq->bh->b_data;
}


If anyone has a better solution I would be glad to hear it. Failing that
I'll submit this in normal kernel patch format as soon as I've worked
out how...

Regards,
Chris R.
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