Re: Fw: crash on x86_64 - mm related?

On Thu, 1 Dec 2005, Hugh Dickins wrote:

...
> Nick and I had already been looking at drivers/scsi/{sg.c,st.c},
> brought there by __put_page in sg.c's peculiar sg_rb_correct4mmap,
> which we'd like to remove. But that's irrelevant to your pain, except...
>
> One extract from the patches I'd like to send Doug and Kai for 2.6.15
> or 2.6.16 is this below: since the incomplete get_user_pages path omits
> to reset res, but has already released all the pages, it will result in
> premature freeing of user pages, and behaviour just like you've seen.
>
> Though I'd have thought incomplete get_user_pages was an exceptional
> case, and a bit surprised you'd encounter it. Perhaps there's some
> other premature freeing in the driver, and this instance has nothing
> whatever to do with it.
>
> If the problem were easily reproducible, it'd be great if you could
> try this patch; but I think you've said it's not :-(
>
> Hugh
>
> --- 2.6.14/drivers/scsi/st.c 2005-10-28 01:02:08.000000000 +0100
> +++ linux/drivers/scsi/st.c 2005-12-01 20:06:02.000000000 +0000
> @@ -4511,6 +4511,7 @@ static int sgl_map_user_pages(struct sca
> if (res > 0) {
> for (j=0; j < res; j++)
> page_cache_release(pages[j]);
> + res = 0;
> }
> kfree(pages);
> return res;
>
Whether this fix solves the current problem or not, it clearly fixes a
bug. If someone wants to include this into a patch series, you can add
Signed-off-by: Kai Makisara <kai.makisara@xxxxxxxxxxx>
If not, I will include this when I send patches next time.

Thanks for noticing this problem.

Kai

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