Resolve stall when disk full affects validator block state writes.

include/bitcoin/node/chase.hpp

@@ -53,6 +53,10 @@ enum class chase
     /// Issued by 'full_node' and handled by 'check', 'validate', 'confirm'.
     resume,
 
+    /// Node is recovering from disk full condition.
+    /// Issued by 'storage' and handled by 'validate'.
+    unfull,
+
     /// Channel starved for work (object_t).
     /// Issued by 'block_in_31800' and handled by 'session_outbound'.
     starved,

include/bitcoin/node/chasers/chaser_validate.hpp

@@ -143,6 +143,7 @@ class BCN_API chaser_validate
     std::atomic<size_t> validate_backlog_{};
     std::atomic<size_t> batch_backlog_{};
     std::atomic_bool maximum_posted_{};
+    std::atomic_bool recovering_{};
 
     network::asio::strand validation_strand_;
     const uint32_t subsidy_interval_;

src/chasers/chaser_storage.cpp

@@ -156,6 +156,9 @@ void chaser_storage::do_reload() NOEXCEPT
     }
     else
     {
+        // Recovery from disk full message sent in addition to chase::resume.
+        notify(error::success, chase::unfull, {});
+
         resume();
         const auto span = duration_cast<seconds>(logger::now() - start);
         LOGN("Reload from disk full complete in " << span.count() << " secs.");

src/chasers/chaser_validate.cpp

@@ -71,6 +71,14 @@ bool chaser_validate::handle_chase(const code&, chase event_,
     if (closed())
         return false;
 
+    // Latch recovering from disk full, before suspension is lifted.
+    // Because in-flight blocks are lost, reset position when backlog clears.
+    if (event_ == chase::unfull)
+    {
+        recovering_.store(true);
+        return true;
+    }
+
     // Stop generating query during suspension.
     // Incoming events may already be flushed to the strand at this point.
     if (suspended())
@@ -138,6 +146,12 @@ void chaser_validate::do_bump(height_t) NOEXCEPT
 {
     BC_ASSERT(stranded());
 
+    if (recovering_.load() && is_zero(validate_backlog_.load()))
+    {
+        recovering_.store(false);
+        set_position(archive().get_fork());
+    }
+
     const auto height = add1(position());
     if (archive().is_validateable(height))
         do_bumped(height);
@@ -257,19 +271,10 @@ void chaser_validate::complete_block(const code& ec, const header_link& link,
     // Batch jobs (all posting from unstranded).
     // ------------------------------------------------------------------------
 
-    // Avoid posting new work when closing.
-    if (closed() || !batch_enabled_)
+    // Faulted implies disk full prevented threshold batch writes.
+    if (closed() || !batch_enabled_ || faulted)
         return;
 
-    // TODO: ensure doesn't lead to tight revalidation loop under disk full.
-    // Retry faulted threshold, re-enters backlog (presumes disk full).
-    if (faulted)
-    {
-        ++validate_backlog_;
-        POST(post_block, link, bypass);
-        return;
-    }
-
     // Queue block and process batch if ready.
     if (batched)
     {