From 0bd9c87010e25634ea6a91c65c2ff8088372340d Mon Sep 17 00:00:00 2001
From: Dominik Csapak <d.csapak@proxmox.com>
Date: Thu, 2 Jun 2022 16:27:44 +0200
Subject: [PATCH] datastore: lookup: reuse ChunkStore on stale datastore
 re-open

When re-opening a datastore due to the cached entry being stale
(config change) but also if the last re-open was >60s ago). On
datastore open the chunk store was also re-opened, which in turn
creates a new ProcessLocker, loosing any existing shared lock which
can cause conflicts between long running (24h+) backups  and GC.

To fix this, reuse the existing ChunkStore, and thus  its
ProcessLocker, when creating a up-to-date datastore instance on
lookup, since only the datastore config should be reloaded. This is
fine as the ChunkStore path is not updatable over our API.

This was always a potential issue but got exposed in practice by
commit 118deb4db8e709b02704bc66c0551bfa7e4369ed which introduced the
unconditional "re-open after 60s" mechanism.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
 [ T: reword commit message a bit and reference commit that made the
   issue much more likely ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
 pbs-datastore/src/datastore.rs | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index 8bf09ca2..93a5b749 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -145,16 +145,20 @@ impl DataStore {
         let mut map = DATASTORE_MAP.lock().unwrap();
         let entry = map.get(name);
 
-        if let Some(datastore) = &entry {
+        // reuse chunk_store, we only want to reload the datastore config, and the path
+        // is normally not editable and requires a restart of the proxy
+        let chunk_store = if let Some(datastore) = &entry {
             if datastore.last_generation == generation && now < (datastore.last_update + 60) {
                 return Ok(Arc::new(Self {
                     inner: Arc::clone(datastore),
                     operation,
                 }));
             }
-        }
+            Arc::clone(&datastore.chunk_store)
+        } else {
+            Arc::new(ChunkStore::open(name, &config.path)?)
+        };
 
-        let chunk_store = ChunkStore::open(name, &config.path)?;
         let datastore = DataStore::with_store_and_config(chunk_store, config, generation, now)?;
 
         let datastore = Arc::new(datastore);
@@ -198,7 +202,12 @@ impl DataStore {
         let name = config.name.clone();
 
         let chunk_store = ChunkStore::open(&name, &config.path)?;
-        let inner = Arc::new(Self::with_store_and_config(chunk_store, config, 0, 0)?);
+        let inner = Arc::new(Self::with_store_and_config(
+            Arc::new(chunk_store),
+            config,
+            0,
+            0,
+        )?);
 
         if let Some(operation) = operation {
             update_active_operations(&name, operation, 1)?;
@@ -208,7 +217,7 @@ impl DataStore {
     }
 
     fn with_store_and_config(
-        chunk_store: ChunkStore,
+        chunk_store: Arc<ChunkStore>,
         config: DataStoreConfig,
         last_generation: usize,
         last_update: i64,
@@ -235,7 +244,7 @@ impl DataStore {
         let chunk_order = tuning.chunk_order.unwrap_or(ChunkOrder::Inode);
 
         Ok(DataStoreImpl {
-            chunk_store: Arc::new(chunk_store),
+            chunk_store,
             gc_mutex: Mutex::new(()),
             last_gc_status: Mutex::new(gc_status),
             verify_new: config.verify_new.unwrap_or(false),