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Re: [dm-devel] [PATCH 0/8] dm: request-based dm-multipath



Hi Hannes,

On 2009/03/10 16:17 +0900, Hannes Reinecke wrote:
>>>>>   o kernel panic occurs by frequent table swapping during heavy I/Os.
>>>>>  
>>>> That's probably fixed by this patch:
>>>>
>>>> --- linux-2.6.27/drivers/md/dm.c.orig   2009-01-23
>>>> 15:59:22.741461315 +0100
>>>> +++ linux-2.6.27/drivers/md/dm.c        2009-01-26
>>>> 09:03:02.787605723 +0100
>>>> @@ -714,13 +714,14 @@ static void free_bio_clone(struct reques
>>>>         struct dm_rq_target_io *tio = clone->end_io_data;
>>>>         struct mapped_device *md = tio->md;
>>>>         struct bio *bio;
>>>> -       struct dm_clone_bio_info *info;
>>>>  
>>>>         while ((bio = clone->bio) != NULL) {
>>>>                 clone->bio = bio->bi_next;
>>>>  
>>>> -               info = bio->bi_private;
>>>> -               free_bio_info(md, info);
>>>> +               if (bio->bi_private) {
>>>> +                       struct dm_clone_bio_info *info =
>>>> bio->bi_private;
>>>> +                       free_bio_info(md, info);
>>>> +               }
>>>>  
>>>>                 bio->bi_private = md->bs;
>>>>                 bio_put(bio);
>>>>
>>>> The info field is not necessarily filled here, so we have to check
>>>> for it
>>>> explicitly.
>>>>
>>>> With these two patches request-based multipathing have survived all
>>>> stress-tests
>>>> so far. Except on mainframe (zfcp), but that's more a driver-related
>>>> thing.
>>
>> Do you hit some problem without the patch above?
>> If so, that should be a programming bug and we need to fix it. 
>> Otherwise,
>> we should be leaking a memory (since all cloned bio should always have
>> the dm_clone_bio_info structure in ->bi_private).
>>
> Yes, I've found that one later on.
> The real problem was in clone_setup_bios(), which might end up calling an
> invalid end_io_data pointer. Patch is attached.

Nice catch!  Thank you for the patch.

> -static void free_bio_clone(struct request *clone)
> +static void free_bio_clone(struct request *clone, struct mapped_device *md)

I have changed the argument order to match with other free_* functions:
    free_bio_clone(struct mapped_device *md, struct request *clone)

Thanks,
Kiyoshi Ueda


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