[Qemu-devel] [PATCH 0/2] dirty bitmap fixes

[Qemu-devel] [PATCH 0/2] dirty bitmap fixes

[Vladimir Sementsov-Ogievskiy]

Vladimir Sementsov-Ogievskiy (2):
  block/dirty-bitmap: add bdrv_enable_dirty_bitmap_locked
  dirty-bitmap: fix double lock on bitmap enabling

 include/block/dirty-bitmap.h   |  1 +
 block/dirty-bitmap.c           | 12 +++++++++---
 migration/block-dirty-bitmap.c |  4 ++--
 3 files changed, 12 insertions(+), 5 deletions(-)

-- 
2.11.1

[Qemu-devel] [PATCH 1/2] block/dirty-bitmap: add bdrv_enable_dirty_bitmap_locked

[Vladimir Sementsov-Ogievskiy]

Add _locked version of bdrv_enable_dirty_bitmap, to fix dirty bitmap
migration in the following patch.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 include/block/dirty-bitmap.h | 1 +
 block/dirty-bitmap.c         | 9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
index 288dc6adb6..259bd27c40 100644
--- a/include/block/dirty-bitmap.h
+++ b/include/block/dirty-bitmap.h
@@ -32,6 +32,7 @@ void bdrv_remove_persistent_dirty_bitmap(BlockDriverState *bs,
                                          Error **errp);
 void bdrv_disable_dirty_bitmap(BdrvDirtyBitmap *bitmap);
 void bdrv_enable_dirty_bitmap(BdrvDirtyBitmap *bitmap);
+void bdrv_enable_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap);
 BlockDirtyInfoList *bdrv_query_dirty_bitmaps(BlockDriverState *bs);
 uint32_t bdrv_get_default_bitmap_granularity(BlockDriverState *bs);
 uint32_t bdrv_dirty_bitmap_granularity(const BdrvDirtyBitmap *bitmap);
diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index db1782ec1f..93744b3565 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -241,6 +241,12 @@ int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
     return 0;
 }
 
+void bdrv_enable_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap)
+{
+    assert(!bdrv_dirty_bitmap_frozen(bitmap));
+    bitmap->disabled = false;
+}
+
 /* Called with BQL taken. */
 void bdrv_dirty_bitmap_enable_successor(BdrvDirtyBitmap *bitmap)
 {
@@ -424,8 +430,7 @@ void bdrv_disable_dirty_bitmap(BdrvDirtyBitmap *bitmap)
 void bdrv_enable_dirty_bitmap(BdrvDirtyBitmap *bitmap)
 {
     bdrv_dirty_bitmap_lock(bitmap);
-    assert(!bdrv_dirty_bitmap_frozen(bitmap));
-    bitmap->disabled = false;
+    bdrv_enable_dirty_bitmap_locked(bitmap);
     bdrv_dirty_bitmap_unlock(bitmap);
 }
 
-- 
2.11.1

[Qemu-devel] [PATCH 2/2] dirty-bitmap: fix double lock on bitmap enabling

[Vladimir Sementsov-Ogievskiy]

Bitmap lock/unlock were added to bdrv_enable_dirty_bitmap in
8b1402ce80d, but some places were not updated correspondingly, which
leads to trying to take this lock twice, which is dead-lock. Fix this.

Actually, iotest 199 (about dirty bitmap postcopy migration) is broken
now, and this fixes it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 block/dirty-bitmap.c           | 3 ++-
 migration/block-dirty-bitmap.c | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 93744b3565..c9b8a6fd52 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -250,8 +250,9 @@ void bdrv_enable_dirty_bitmap_locked(BdrvDirtyBitmap *bitmap)
 /* Called with BQL taken. */
 void bdrv_dirty_bitmap_enable_successor(BdrvDirtyBitmap *bitmap)
 {
+    assert(bitmap->mutex == bitmap->successor->mutex);
     qemu_mutex_lock(bitmap->mutex);
-    bdrv_enable_dirty_bitmap(bitmap->successor);
+    bdrv_enable_dirty_bitmap_locked(bitmap->successor);
     qemu_mutex_unlock(bitmap->mutex);
 }
 
diff --git a/migration/block-dirty-bitmap.c b/migration/block-dirty-bitmap.c
index 3bafbbdc4c..477826330c 100644
--- a/migration/block-dirty-bitmap.c
+++ b/migration/block-dirty-bitmap.c
@@ -511,7 +511,7 @@ void dirty_bitmap_mig_before_vm_start(void)
         DirtyBitmapLoadBitmapState *b = item->data;
 
         if (b->migrated) {
-            bdrv_enable_dirty_bitmap(b->bitmap);
+            bdrv_enable_dirty_bitmap_locked(b->bitmap);
         } else {
             bdrv_dirty_bitmap_enable_successor(b->bitmap);
         }
@@ -547,7 +547,7 @@ static void dirty_bitmap_load_complete(QEMUFile *f, DirtyBitmapLoadState *s)
         if (enabled_bitmaps == NULL) {
             /* in postcopy */
             bdrv_reclaim_dirty_bitmap_locked(s->bs, s->bitmap, &error_abort);
-            bdrv_enable_dirty_bitmap(s->bitmap);
+            bdrv_enable_dirty_bitmap_locked(s->bitmap);
         } else {
             /* target not started, successor must be empty */
             int64_t count = bdrv_get_dirty_count(s->bitmap);
-- 
2.11.1

Re: [Qemu-devel] [PATCH 0/2] dirty bitmap fixes

[John Snow]

On 06/25/2018 12:57 PM, Vladimir Sementsov-Ogievskiy wrote:
> Vladimir Sementsov-Ogievskiy (2):
>   block/dirty-bitmap: add bdrv_enable_dirty_bitmap_locked
>   dirty-bitmap: fix double lock on bitmap enabling
> 
>  include/block/dirty-bitmap.h   |  1 +
>  block/dirty-bitmap.c           | 12 +++++++++---
>  migration/block-dirty-bitmap.c |  4 ++--
>  3 files changed, 12 insertions(+), 5 deletions(-)
> 

ACK,

though it looks really odd that we've got enable/disable but only one
corresponding _locked version.

I have a patch somewhere in my local files to create a combined
_set_disabled() that would cut the number of functions we have by a
little bit.

I'll take this first though, as an iotest fix.

--js

Re: [Qemu-devel] [PATCH 0/2] dirty bitmap fixes

[John Snow]

On 06/25/2018 12:57 PM, Vladimir Sementsov-Ogievskiy wrote:
> Vladimir Sementsov-Ogievskiy (2):
>   block/dirty-bitmap: add bdrv_enable_dirty_bitmap_locked
>   dirty-bitmap: fix double lock on bitmap enabling
> 
>  include/block/dirty-bitmap.h   |  1 +
>  block/dirty-bitmap.c           | 12 +++++++++---
>  migration/block-dirty-bitmap.c |  4 ++--
>  3 files changed, 12 insertions(+), 5 deletions(-)
> 

Thanks, applied to my bitmaps tree:

https://github.com/jnsnow/qemu/commits/bitmaps
https://github.com/jnsnow/qemu.git

--js