promisor-remote: skip move_to_tail when no-op

Previously, when promisor_remote_move_to_tail() is called for a
promisor_remote which is currently the final element in promisors, a
cycle is created in the promisors linked list. This cycle leads to a
double free later on in promisor_remote_clear() when the final element
of the promisors list is removed: promisors is set to promisors->next (a
no-op, as promisors->next == promisors); the previous value of promisors
is free()'d; then the new value of promisors (which is equal to the
previous value of promisors) is also free()'d. This double-free error
was unrecoverable for the user without removing the filter or re-cloning
the repo and hoping to miss this edge case.

Now, when promisor_remote_move_to_tail() would be a no-op, just do a
no-op. In cases of promisor_remote_move_to_tail() where r is not already
at the tail of the list, it works as before.

Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Acked-by: Christian Couder <christian.couder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/promisor-remote.c b/promisor-remote.c
index 9bc296cdde2acc3871c0738533decb70c69f1b62..9bd5b79d59446dede45ea075fc8d7307fcb98648 100644 (file)
--- a/promisor-remote.c
+++ b/promisor-remote.c
@@ -89,6 +89,9 @@ static struct promisor_remote *promisor_remote_lookup(const char *remote_name,
 static void promisor_remote_move_to_tail(struct promisor_remote *r,
                                         struct promisor_remote *previous)
 {
+       if (r->next == NULL)
+               return;
+
        if (previous)
                previous->next = r->next;
        else

diff --git a/t/t0410-partial-clone.sh b/t/t0410-partial-clone.sh
index 2498e72a3412da9bc22f27e33df7d2380e62ad5e..c5b2018a302fced54f435224950ff8ecad15c82f 100755 (executable)
--- a/t/t0410-partial-clone.sh
+++ b/t/t0410-partial-clone.sh
@@ -429,6 +429,19 @@ test_expect_success 'rev-list dies for missing objects on cmd line' '
        done
 '
 
+test_expect_success 'single promisor remote can be re-initialized gracefully' '
+       # ensure one promisor is in the promisors list
+       rm -rf repo &&
+       test_create_repo repo &&
+       test_create_repo other &&
+       git -C repo remote add foo "file://$(pwd)/other" &&
+       git -C repo config remote.foo.promisor true &&
+       git -C repo config extensions.partialclone foo &&
+
+       # reinitialize the promisors list
+       git -C repo fetch --filter=blob:none foo
+'
+
 test_expect_success 'gc repacks promisor objects separately from non-promisor objects' '
        rm -rf repo &&
        test_create_repo repo &&