ext4: correct the judgment of BUG in ext4_mb_normalize_request

ext4_mb_normalize_request() can move logical start of allocated blocks
to reduce fragmentation and better utilize preallocation. However logical
block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
always be covered by allocated blocks so we should check that by
modifying and to or in the assertion.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20220528110017.354175-3-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 4d3740fdff90f558fbb3aff096a5efc70ec8e209..9e06334771a394fb0cb60615a22af507b19c25d9 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4185,7 +4185,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
        }
        rcu_read_unlock();
 
-       if (start + size <= ac->ac_o_ex.fe_logical &&
+       /*
+        * In this function "start" and "size" are normalized for better
+        * alignment and length such that we could preallocate more blocks.
+        * This normalization is done such that original request of
+        * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
+        * "size" boundaries.
+        * (Note fe_len can be relaxed since FS block allocation API does not
+        * provide gurantee on number of contiguous blocks allocation since that
+        * depends upon free space left, etc).
+        * In case of inode pa, later we use the allocated blocks
+        * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
+        * range of goal/best blocks [start, size] to put it at the
+        * ac_o_ex.fe_logical extent of this inode.
+        * (See ext4_mb_use_inode_pa() for more details)
+        */
+       if (start + size <= ac->ac_o_ex.fe_logical ||
                        start > ac->ac_o_ex.fe_logical) {
                ext4_msg(ac->ac_sb, KERN_ERR,
                         "start %lu, size %lu, fe_logical %lu",