accel/tcg: Properly unlink a TB linked to itself

When we remove dest from orig's links, we lose the link
that we rely on later to reset links.  This can lead to
failure to release from spinlock with self-modifying code.

Cc: qemu-stable@nongnu.org
Reported-by: 李威威 <liweiwei@kubuds.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Anton Johansson <anjo@rev.ng>
Tested-by: Anton Johansson <anjo@rev.ng>
(cherry picked from commit 03fe665980)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

accel/tcg/tb-maint.c

@@ -839,6 +839,14 @@ static inline void tb_remove_from_jmp_list(TranslationBlock *orig, int n_orig)
      * We first acquired the lock, and since the destination pointer matches,
      * we know for sure that @orig is in the jmp list.
      */
+    if (dest == orig) {
+        /*
+         * In the case of a TB that links to itself, removing the entry
+         * from the list means that it won't be present later during
+         * tb_jmp_unlink -- unlink now.
+         */
+        tb_reset_jump(orig, n_orig);
+    }
     pprev = &dest->jmp_list_head;
     TB_FOR_EACH_JMP(dest, tb, n) {
         if (tb == orig && n == n_orig) {