dm io: delay dec_count

Delay decrementing the 'struct io' reference count until after the bio has
been freed so that a bio destructor function may reference it.  Required by a
later patch.

Signed-off-by: Heinz Mauelshagen <hjm@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: Milan Broz <mbroz@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 8bdc8a87b249..4d19c45158b4 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -126,7 +126,8 @@ static void dec_count(struct io *io, unsigned int region, int error)
 
 static int endio(struct bio *bio, unsigned int done, int error)
 {
-        struct io *io = (struct io *) bio->bi_private;
+        struct io *io;
+        unsigned region;
 
         /* keep going until we've finished */
         if (bio->bi_size)
@@ -135,10 +136,17 @@ static int endio(struct bio *bio, unsigned int done, int error)
         if (error && bio_data_dir(bio) == READ)
                 zero_fill_bio(bio);
 
-        dec_count(io, bio_get_region(bio), error);
+        /*
+         * The bio destructor in bio_put() may use the io object.
+         */
+        io = bio->bi_private;
+        region = bio_get_region(bio);
+
         bio->bi_max_vecs++;
         bio_put(bio);
 
+        dec_count(io, region, error);
+
         return 0;
 }