Messages in this thread | | | Date | Wed, 13 Mar 2002 09:09:46 +0100 | From | Jens Axboe <> | Subject | Re: Linux 2.4.19-pre3 |
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On Tue, Mar 12 2002, Marcelo Tosatti wrote: > So, Jens, could you please explain the problem in the interrupt handlers > in detail ?
Ok... It affects all the pio handlers in ide-taskfile.c, multi-write/read as well. The address for pio transfers is calculated like so:
va = rq->buffer + (rq->nr_sectors - rq->current_nr_sectors) * SECTOR_SIZE;
which is wrong for two reasons. First of all, rq->buffer cannot be indexed for the entire nr_sectors range -- it's per definition only the first segment in the request, and can as such only be indexed within the first current_nr_sectors number of sectors. The above can be grossly out of range... Second, nr_sectors and current_nr_sectors are indexing two different things -- the former indexes the entire request (all segments) while the latter indexes only the first segments. So
foo = rq->nr_sectors - rq->current_nr_sectors;
makes no sense _at all_ and can only be wrong.
So why does 2.4.19-pre3 work for pio at all? For the same reason that Andre never found this problem in 2.5 either: the taskfile interrupt handlers are _never_ used in pio mode. In 2.5 it was by accident, and when the merge happened they did indeed get used. It ate disks, very quickly. Take a look at drivers/ide/ide-disk.c, line 64:
#ifdef CONFIG_IDE_TASKFILE_IO # undef __TASKFILE__IO /* define __TASKFILE__IO */ #else /* CONFIG_IDE_TASKFILE_IO */ # undef __TASKFILE__IO #endif /* CONFIG_IDE_TASKFILE_IO */
It's a mess... This really should have been fixed prior to 2.4 inclusion. Oh well.
-- Jens Axboe
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