Make buf_shrink_freelists warn, not crash, when n_to_skip is too high

This mitigates bug 1125, but doesn't fix its root cause (whatever
that is).

1 files changed, 15 insertions, 4 deletions

diff --git a/src/or/buffers.c b/src/or/buffers.c
index 3ba2760bf..e8422637c 100644
--- a/src/or/buffers.c
+++ b/src/or/buffers.c
@@ -270,14 +270,25 @@ buf_shrink_freelists(int free_all)
         (freelists[i].lowest_length - slack);
       int n_to_skip = freelists[i].cur_length - n_to_free;
       int orig_n_to_free = n_to_free, n_freed=0;
+      int orig_n_to_skip = n_to_skip;
       int new_length = n_to_skip;
       chunk_t **chp = &freelists[i].head;
       chunk_t *chunk;
-      log_info(LD_MM, "Cleaning freelist for %d-byte chunks: keeping %d, "
-               "dropping %d.",
-               (int)freelists[i].alloc_size, n_to_skip, n_to_free);
+      log_info(LD_MM, "Cleaning freelist for %d-byte chunks: length %d, "
+               "keeping %d, dropping %d.",
+               (int)freelists[i].alloc_size, freelists[i].cur_length,
+               n_to_skip, n_to_free);
+      tor_assert(n_to_skip + n_to_free == freelists[i].cur_length);
       while (n_to_skip) {
-        tor_assert((*chp)->next);
+        if (! (*chp)->next) {
+          log_warn(LD_BUG, "I wanted to skip %d chunks in the freelist for "
+                   "%d-byte chunks, but only found %d. (Length %d)",
+                   orig_n_to_skip, (int)freelists[i].alloc_size,
+                   orig_n_to_skip-n_to_skip, freelists[i].cur_length);
+          assert_freelist_ok(&freelists[i]);
+          return;
+        }
+        // tor_assert((*chp)->next);
         chp = &(*chp)->next;
         --n_to_skip;
       }