[Qemu-devel] [RFC V7 24/32] qcow2: Serialize write requests when deduplication is activated.

["Benoît Canet" <benoit@irqsave.net>]

This fixes the sub cluster sized writes race conditions while waiting
for a faster solution.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 block/qcow2.c |   17 ++++++++++++++++-
 block/qcow2.h |    1 +
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 838241c..9c613e5 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -515,6 +515,7 @@ static int qcow2_open(BlockDriverState *bs, int flags)
 
     /* Initialise locks */
     qemu_co_mutex_init(&s->lock);
+    qemu_co_mutex_init(&s->dedup_lock);
 
     /* Repair image if dirty */
     if (!(flags & BDRV_O_CHECK) && !bs->read_only &&
@@ -805,9 +806,19 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
 
     s->cluster_cache_offset = -1; /* disable compressed cache */
 
+    atomic_dedup_is_running = qcow2_dedup_is_running(bs);
+
+    if (atomic_dedup_is_running) {
+        /* This mutex is used to serialize the write requests in the dedup case.
+         * The goal is to avoid that the dedup process concurrents requests to
+         * the same clusters and corrupt data.
+         * With qcow2_dedup_read_missing_and_concatenate that would not work.
+         */
+        qemu_co_mutex_lock(&s->dedup_lock);
+    }
+
     qemu_co_mutex_lock(&s->lock);
 
-    atomic_dedup_is_running = qcow2_dedup_is_running(bs);
     if (atomic_dedup_is_running) {
         QTAILQ_INIT(&ds.undedupables);
         ds.phash.reuse = false;
@@ -977,6 +988,10 @@ fail:
         g_free(l2meta);
     }
 
+    if (atomic_dedup_is_running) {
+        qemu_co_mutex_unlock(&s->dedup_lock);
+    }
+
     qemu_iovec_destroy(&hd_qiov);
     qemu_vfree(cluster_data);
     qemu_vfree(dedup_cluster_data);
diff --git a/block/qcow2.h b/block/qcow2.h
index b858db9..a430fe1 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -236,6 +236,7 @@ typedef struct BDRVQcowState {
     GTree *dedup_tree_by_hash;
 
     CoMutex lock;
+    CoMutex dedup_lock;
 
     uint32_t crypt_method; /* current crypt method, 0 if no key yet */
     uint32_t crypt_method_header;
-- 
1.7.10.4