From: Mikulas Patocka Accept empty barriers in dm-io. dm-io will process empty write barrier requests just like the other read/write requests. Signed-off-by: Mikulas Patocka Signed-off-by: Alasdair G Kergon --- drivers/md/dm-io.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) Index: linux-2.6.30/drivers/md/dm-io.c =================================================================== --- linux-2.6.30.orig/drivers/md/dm-io.c +++ linux-2.6.30/drivers/md/dm-io.c @@ -286,7 +286,11 @@ static void do_region(int rw, unsigned r unsigned num_bvecs; sector_t remaining = where->count; - while (remaining) { + /* + * where->count may be zero if rw holds a write barrier and we + * need to send a zero-sized barrier. + */ + do { /* * Allocate a suitably sized-bio: we add an extra * bvec for bio_get/set_region() and decrement bi_max_vecs @@ -323,7 +327,7 @@ static void do_region(int rw, unsigned r atomic_inc(&io->count); submit_bio(rw, bio); - } + } while (remaining); } static void dispatch_io(int rw, unsigned int num_regions, @@ -342,7 +346,7 @@ static void dispatch_io(int rw, unsigned */ for (i = 0; i < num_regions; i++) { *dp = old_pages; - if (where[i].count) + if (where[i].count || (rw & (1 << BIO_RW_BARRIER))) do_region(rw, i, where + i, dp, io); }