ext4: fix locking typo in mballoc which could cause soft lockup hangs

Smatch (http://repo.or.cz/w/smatch.git/) complains about the locking in
ext4_mb_add_n_trim() from fs/ext4/mballoc.c

  4438          list_for_each_entry_rcu(tmp_pa, &lg->lg_prealloc_list[order],
  4439                                                  pa_inode_list) {
  4440                  spin_lock(&tmp_pa->pa_lock);
  4441                  if (tmp_pa->pa_deleted) {
  4442                          spin_unlock(&pa->pa_lock);
  4443                          continue;
  4444                  }

Brown paper bag time...

Reported-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5f3e3a3..f871677 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4392,7 +4392,7 @@ static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
                                                pa_inode_list) {
                spin_lock(&tmp_pa->pa_lock);
                if (tmp_pa->pa_deleted) {
-                       spin_unlock(&pa->pa_lock);
+                       spin_unlock(&tmp_pa->pa_lock);
                        continue;
                }
                if (!added && pa->pa_free < tmp_pa->pa_free) {