[Qemu-devel] [PATCH v2] block/vdi: Add locking for parallel requests

[Max Reitz]

Concurrently modifying the bmap does not seem to be a good idea; this patch adds
a lock for it. See https://bugs.launchpad.net/qemu/+bug/1422307 for what
can go wrong without.

Cc: qemu-stable <qemu-sta...@nongnu.org>
Signed-off-by: Max Reitz <mre...@redhat.com>
---
v2:
- Make the mutex cover vdi_co_write() completely [Kevin]
- Add a TODO comment [Kevin]
---
 block/vdi.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/block/vdi.c b/block/vdi.c
index 74030c6..f5f42ef 100644
--- a/block/vdi.c
+++ b/block/vdi.c
@@ -51,6 +51,7 @@
 
 #include "qemu-common.h"
 #include "block/block_int.h"
+#include "block/coroutine.h"
 #include "qemu/module.h"
 #include "migration/migration.h"
 
@@ -196,6 +197,8 @@ typedef struct {
     /* VDI header (converted to host endianness). */
     VdiHeader header;
 
+    CoMutex bmap_lock;
+
     Error *migration_blocker;
 } BDRVVdiState;
 
@@ -498,6 +501,8 @@ static int vdi_open(BlockDriverState *bs, QDict *options, 
int flags,
         goto fail_free_bmap;
     }
 
+    qemu_co_mutex_init(&s->bmap_lock);
+
     /* Disable migration when vdi images are used */
     error_set(&s->migration_blocker,
               QERR_BLOCK_FORMAT_FEATURE_NOT_SUPPORTED,
@@ -607,6 +612,9 @@ static int vdi_co_write(BlockDriverState *bs,
 
     logout("\n");
 
+    /* TODO: Figure out why this is necessary */
+    qemu_co_mutex_lock(&s->bmap_lock);
+
     while (ret >= 0 && nb_sectors > 0) {
         block_index = sector_num / s->block_sectors;
         sector_in_block = sector_num % s->block_sectors;
@@ -656,6 +664,7 @@ static int vdi_co_write(BlockDriverState *bs,
 
     logout("finished data write\n");
     if (ret < 0) {
+        qemu_co_mutex_unlock(&s->bmap_lock);
         return ret;
     }
 
@@ -674,6 +683,7 @@ static int vdi_co_write(BlockDriverState *bs,
         block = NULL;
 
         if (ret < 0) {
+            qemu_co_mutex_unlock(&s->bmap_lock);
             return ret;
         }
 
@@ -690,6 +700,7 @@ static int vdi_co_write(BlockDriverState *bs,
         ret = bdrv_write(bs->file, offset, base, n_sectors);
     }
 
+    qemu_co_mutex_unlock(&s->bmap_lock);
     return ret;
 }
 
-- 
2.1.0