Decref CacheFileRegion after read is done not before (elastic#102848)

The CacheFileRegion instance is decref before the read operation is executed, meaning that the SharedBytes.IO instance can return to the pool of free regions, being polled and written by another thread for another cache file region, before the first read is effectively completed (and will return incorrect bytes).
tlrx · Dec 8, 2023 · 1edcee8 · 1edcee8
1 parent 479fcef
commit 1edcee8
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diff --git a/docs/changelog/102848.yaml b/docs/changelog/102848.yaml
@@ -0,0 +1,5 @@
+pr: 102848
+summary: Decref `SharedBytes.IO` after read is done not before
+area: Snapshot/Restore
+type: bug
+issues: []
diff --git a/...n/blob-cache/src/main/java/org/elasticsearch/blobcache/shared/SharedBlobCacheService.java b/...n/blob-cache/src/main/java/org/elasticsearch/blobcache/shared/SharedBlobCacheService.java
@@ -915,7 +915,7 @@ void populateAndRead(
                 final List<SparseFileTracker.Gap> gaps = tracker.waitForRange(
                     rangeToWrite,
                     rangeToRead,
-                    ActionListener.runBefore(listener, resource::close).delegateFailureAndWrap((l, success) -> {
+                    ActionListener.runAfter(listener, resource::close).delegateFailureAndWrap((l, success) -> {
                         var ioRef = io;
                         assert regionOwners.get(ioRef) == this;
                         final int start = Math.toIntExact(rangeToRead.start());