btrfs: make sure we stay inside the bvec during __btrfs_lookup_bio_sums

Commit c40a3d38aff4e1c (Btrfs: Compute and look up csums based on
sectorsized blocks) changes around how we walk the bios while looking up
crcs.  There's an inner loop that is jumping to the next bvec based on
sectors and before it derefs the next bvec, it needs to make sure we're
still in the bio.

In this case, the outer loop would have decided to stop moving forward
too, and the bvec deref is never actually used for anything.  But
CONFIG_DEBUG_PAGEALLOC catches it because we're outside our bio.

Signed-off-by: Chris Mason <clm@fb.com>
Reviewed-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 763fd170ff1656fedce3dd37fc68a492d7c8f711..b5baf5bdc8e183df9fd697eda5a7d2d16b97baa0 100644 (file)
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -292,12 +292,22 @@ found:
                        page_bytes_left -= root->sectorsize;
                        if (!page_bytes_left) {
                                bio_index++;
+                               /*
+                                * make sure we're still inside the
+                                * bio before we update page_bytes_left
+                                */
+                               if (bio_index >= bio->bi_vcnt) {
+                                       WARN_ON_ONCE(count);
+                                       goto done;
+                               }
                                bvec++;
                                page_bytes_left = bvec->bv_len;
                        }
 
                }
        }
+
+done:
        btrfs_free_path(path);
        return 0;
 }