From e309436319ed5cbc3aaf53221070a1fd070b8bcf Mon Sep 17 00:00:00 2001
From: Edward Wang <ewang@cloudflare.com>
Date: Mon, 11 Nov 2024 18:09:55 -0800
Subject: Release cache lock after proxy upstream filter, serve stale

The cache locks may be held after serving stale, proxy upstream filter,
or revalidate uncacheable resulting in dangling cache locks.
Also only disable cache on final error if cache was not already
disabled, and add DeclinedToUpstream / UpstreamError no cache reasons.
---
 pingora-proxy/src/lib.rs         | 17 ++++++++++++++++-
 pingora-proxy/src/proxy_cache.rs | 17 ++++++++++++++++-
 pingora-proxy/src/proxy_h2.rs    |  1 +
 3 files changed, 33 insertions(+), 2 deletions(-)

(limited to 'pingora-proxy')

diff --git a/pingora-proxy/src/lib.rs b/pingora-proxy/src/lib.rs
index f13a1f7..731cdb4 100644
--- a/pingora-proxy/src/lib.rs
+++ b/pingora-proxy/src/lib.rs
@@ -535,6 +535,10 @@ impl<SV> HttpProxy<SV> {
                 if !proxy_to_upstream {
                     // The hook can choose to write its own response, but if it doesn't, we respond
                     // with a generic 502
+                    if session.cache.enabled() {
+                        // drop the cache lock that this request may be holding onto
+                        session.cache.disable(NoCacheReason::DeclinedToUpstream);
+                    }
                     if session.response_written().is_none() {
                         match session.write_response_header_ref(&BAD_GATEWAY).await {
                             Ok(()) => {}
@@ -557,6 +561,10 @@ impl<SV> HttpProxy<SV> {
                 /* else continue */
             }
             Err(e) => {
+                if session.cache.enabled() {
+                    session.cache.disable(NoCacheReason::InternalError);
+                }
+
                 self.handle_error(
                     &mut session,
                     &mut ctx,
@@ -621,7 +629,14 @@ impl<SV> HttpProxy<SV> {
 
         if let Some(e) = final_error.as_ref() {
             // If we have errored and are still holding a cache lock, release it.
-            session.cache.disable(NoCacheReason::InternalError);
+            if session.cache.enabled() {
+                let reason = if *e.esource() == ErrorSource::Upstream {
+                    NoCacheReason::UpstreamError
+                } else {
+                    NoCacheReason::InternalError
+                };
+                session.cache.disable(reason);
+            }
             let status = self.inner.fail_to_proxy(&mut session, e, &mut ctx).await;
 
             // final error will have > 0 status unless downstream connection is dead
diff --git a/pingora-proxy/src/proxy_cache.rs b/pingora-proxy/src/proxy_cache.rs
index 4369ec8..8957bc7 100644
--- a/pingora-proxy/src/proxy_cache.rs
+++ b/pingora-proxy/src/proxy_cache.rs
@@ -667,8 +667,18 @@ impl<SV> HttpProxy<SV> {
                         None,
                         None,
                     );
-                    self.inner
+                    if self
+                        .inner
                         .should_serve_stale(session, ctx, Some(&http_status_error))
+                    {
+                        // no more need to keep the write lock
+                        session
+                            .cache
+                            .release_write_lock(NoCacheReason::UpstreamError);
+                        true
+                    } else {
+                        false
+                    }
                 } else {
                     false // not 304, not stale if error status code
                 }
@@ -712,6 +722,11 @@ impl<SV> HttpProxy<SV> {
             self.inner.request_summary(session, ctx)
         );
 
+        // no more need to hang onto the cache lock
+        session
+            .cache
+            .release_write_lock(NoCacheReason::UpstreamError);
+
         Some(self.proxy_cache_hit(session, ctx).await)
     }
 
diff --git a/pingora-proxy/src/proxy_h2.rs b/pingora-proxy/src/proxy_h2.rs
index ba832b2..a27c559 100644
--- a/pingora-proxy/src/proxy_h2.rs
+++ b/pingora-proxy/src/proxy_h2.rs
@@ -409,6 +409,7 @@ impl<SV> HttpProxy<SV> {
                     .cache_http_task(session, &task, ctx, serve_from_cache)
                     .await
                 {
+                    session.cache.disable(NoCacheReason::StorageError);
                     if serve_from_cache.is_miss_body() {
                         // if the response stream cache body during miss but write fails, it has to
                         // give up the entire request
-- 
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