[PATCH AUTOSEL 5.17 20/20] ext4: correct the judgment of BUG in ext4_mb_normalize_request

Sasha Levin
2022-06-21T21:01:57Z

From: Baokun Li <libaokun1@huawei.com>

[ Upstream commit cf4ff938b47fc5c00b0ccce53a3b50eca9b32281 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/mballoc.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 47a560d60d3e..1f328a5e2e3d 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4171,7 +4171,22 @@ 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",
--
2.35.1