dm log writes: fix bug with too large bios

bio_alloc() can allocate a bio with at most BIO_MAX_PAGES (256) vector
entries.  However, the incoming bio may have more vector entries if it
was allocated by other means.  For example, bcache submits bios with
more than BIO_MAX_PAGES entries.  This results in bio_alloc() failure.

To avoid the failure, change the code so that it allocates bio with at
most BIO_MAX_PAGES entries.  If the incoming bio has more entries,
bio_add_page() will fail and a new bio will be allocated - the code that
handles bio_add_page() failure already exists in the dm-log-writes
target.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Josef Bacik <jbacik@fb,com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org # v4.1+

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
index 4cc78aef9007..ba24f4f37efc 100644
--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -260,7 +260,7 @@ static int log_one_block(struct log_writes_c *lc,
         sector++;
 
         atomic_inc(&lc->io_blocks);
-        bio = bio_alloc(GFP_KERNEL, block->vec_cnt);
+        bio = bio_alloc(GFP_KERNEL, min(block->vec_cnt, BIO_MAX_PAGES));
         if (!bio) {
                 DMERR("Couldn't alloc log bio");
                 goto error;
@@ -282,7 +282,7 @@ static int log_one_block(struct log_writes_c *lc,
                 if (ret != block->vecs[i].bv_len) {
                         atomic_inc(&lc->io_blocks);
                         submit_bio(bio);
-                        bio = bio_alloc(GFP_KERNEL, block->vec_cnt - i);
+                        bio = bio_alloc(GFP_KERNEL, min(block->vec_cnt - i, BIO_MAX_PAGES));
                         if (!bio) {
                                 DMERR("Couldn't alloc log bio");
                                 goto error;