Re: [dm-devel] [PATCH] block: add a bi_error field to struct bio
From: Neil Brown <hidden>
Date: 2015-06-10 02:50:54
Also in:
dm-devel, linux-btrfs
On Wed, 3 Jun 2015 15:42:39 +0200 Christoph Hellwig [off-list ref] 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@lst.de>
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:
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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
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@@ -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 <redacted> (md/raid parts) Thanks, NeilBrown