On 08/31/2016 12:27 AM, Mikulas Patocka wrote:

...

Drop that "#ifdef CONFIG_BCACHE". Anyone should be allowed to create a big 
bio, not just bcache.

Yes. Please, do not hide it behind #ifdef.
If it is in code, it should be enabled always.

There can third party modules or some new code appears and creating strange
config dependence only adds more problems later.

Milan

That one test has no performance impact, there is no need to hide it 
behind #ifdef.

Mikulas

quoted

From: Mikulas Patocka <mpatocka@redhat.com>
Date: Tue, 30 Aug 2016 16:38:42 -0400
Subject: [PATCH] dm crypt: fix error with too large bcache bios

When dm-crypt processes writes, it allocates a new bio in
crypt_alloc_buffer().  The bio is allocated from a bio set and it can
have at most BIO_MAX_PAGES vector entries, however the incoming bio can be
larger if it was allocated by bcache.  If the incoming bio is larger,
bio_alloc_bioset() fails and an error is returned.

To avoid the error, we test for a too large bio in the function
crypt_map() and use dm_accept_partial_bio() to split the bio.
dm_accept_partial_bio() trims the current bio to the desired size and
asks DM core to send another bio with the rest of the data.

This fix is wrapped with a check for CONFIG_BCACHE because there
currently isn't any other code that generates too large bios.  So unless
bcache is configured there is no point wasting time making this check.

Signed-off-by: Mikulas Patocka <mpatocka redhat com>
Cc: stable@vger.kernel.org # v3.16+
---
 drivers/md/dm-crypt.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index eedba67..743f548 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c

@@ -1924,6 +1924,12 @@ static int crypt_map(struct dm_target *ti, struct bio *bio)
 		return DM_MAPIO_REMAPPED;
 	}
 
+#ifdef CONFIG_BCACHE
+	if (unlikely(bio->bi_iter.bi_size > (BIO_MAX_PAGES << PAGE_SHIFT)) &&
+	    bio_data_dir(bio) == WRITE)
+		dm_accept_partial_bio(bio, ((BIO_MAX_PAGES << PAGE_SHIFT) >> SECTOR_SHIFT));
+#endif
+
 	io = dm_per_bio_data(bio, cc->per_bio_data_size);
 	crypt_io_init(io, cc, bio, dm_target_offset(ti, bio->bi_iter.bi_sector));
 	io->ctx.req = (struct skcipher_request *)(io + 1);

-- 
2.7.4 (Apple Git-66)

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