On Wed, 3 Jun 2015 15:42:39 +0200
Christoph Hellwig <hch@xxxxxx> wrote:
> Currently we have two different ways to signal an I/O error on a BIO:
>
> (1) by clearing the BIO_UPTODATE flag
> (2) by returning a Linux errno value to the bi_end_io callback
>
> The first one has the drawback of only communicating a single possible
> error (-EIO), and the second one has the drawback of not beeing persistent
> when bios are queued up, and are not passed along from child to parent
> bio in the ever more popular chaining scenario. Having both mechanisms
> available has the additional drawback of utterly confusing driver authors
> and introducing bugs where various I/O submitters only deal with one of
> them, and the others have to add boilerplate code to deal with both kinds
> of error returns.
>
> So add a new bi_error field to store an errno value directly in struct
> bio and remove the existing mechanisms to clean all this up.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
I really like this clean up.
It is unfortunate that the patch is so big, but I guess it has to be.
It mostly looks good, but review is hard and testing is harder :-(
I found:
> diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> index f80f1af..1bad16f 100644
> --- a/drivers/md/raid1.c
> +++ b/drivers/md/raid1.c
....
> @@ -1800,7 +1799,7 @@ static void end_sync_write(struct bio *bio, int error)
> reschedule_retry(r1_bio);
> else {
> put_buf(r1_bio);
> - md_done_sync(mddev, s, uptodate);
> + md_done_sync(mddev, s, !bio->bi_error);
> }
> }
> }
This introduces a use-after-free. put_buf(r1_bio) can result in bio_put on
'bio'.
It is safe to move the put_buf call after the md_done_sync(), but it is
probably best to leave the 'update' variable as it. i.e. Just change:
- int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
+ int uptodate = !bio->bi_error;
I can't see any other problems with the md changes.
Reviewed-by: NeilBrown <neilb@xxxxxxx> (md/raid parts)
Thanks,
NeilBrown
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