hs_pow: fix error path with outdated assumption

This error path with the "PoW cpuworker returned with no solution.
Will retry soon." message was usually lying. It's concerning
now because we expect to always find a solution no matter how
long it takes, rather than re-enter the solver repeatedly, so any
exit without a solution is a sign of a problem.

In fact when this error path gets hit, we are usually missing a
circuit instead because the request is quite old and the circuits
have been destroyed. This is not an emergency, it's just a sign
of client-side overload.

Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>

diff --git a/src/feature/hs/hs_pow.c b/src/feature/hs/hs_pow.c
index 15152bc6490aa80f525889ae7a1ef770c0f706f9..4f662b58d9e669e779ae948a27ae4d020f0ccd4d 100644 (file)
--- a/src/feature/hs/hs_pow.c
+++ b/src/feature/hs/hs_pow.c
@@ -436,9 +436,11 @@ pow_worker_replyfn(void *work_)
     ip = find_desc_intro_point_by_ident(intro_circ->hs_ident, desc);
 
   if (intro_circ && rend_circ && service_identity_pk && desc && ip &&
-      job->pow_solution_out) { /* successful pow solve, and circs still here */
+      job->pow_solution_out) {
 
+    /* successful pow solve, and circs still here */
     log_info(LD_REND, "Got a PoW solution we like! Shipping it!");
+
     /* Set flag to reflect that the HS we are attempting to rendezvous has PoW
      * defenses enabled, and as such we will need to be more lenient with
      * timing out while waiting for the service-side circuit to be built. */
@@ -451,18 +453,16 @@ pow_worker_replyfn(void *work_)
       intro_circ->hs_currently_solving_pow = 0;
     }
 
-  } else { /* unsuccessful pow solve. put it back on the queue. */
-    log_notice(LD_REND,
-               "PoW cpuworker returned with no solution. Will retry soon.");
+  } else {
+    if (!job->pow_solution_out) {
+      log_warn(LD_REND, "PoW cpuworker returned with no solution");
+    } else {
+      log_info(LD_REND, "PoW solution completed but we can "
+                        "no longer locate its circuit");
+    }
     if (intro_circ) {
       intro_circ->hs_currently_solving_pow = 0;
     }
-    /* We could imagine immediately re-launching a follow-up worker
-     * here too, but for now just let the main intro loop find the
-     * not-being-serviced request and it can start everything again. For
-     * the sake of complexity, maybe that's the best long-term solution
-     * too, and we can tune the cpuworker job to try for longer if we want
-     * to improve efficiency. */
   }
 
   pow_worker_job_free(job);