[Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add/remove

* [Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add/remove
@ 2019-02-12 20:07 John Snow
  2019-02-12 20:16 ` Eric Blake
                   ` (2 more replies)
  0 siblings, 3 replies; 6+ messages in thread
From: John Snow @ 2019-02-12 20:07 UTC (permalink / raw)
  To: qemu-block, qemu-devel
  Cc: Kevin Wolf, vsementsov, Max Reitz, pbonzini, eblake,
	Markus Armbruster, John Snow

When bitmaps are persistent, they may incur a disk read or write when bitmaps
are added or removed. For configurations like virtio-dataplane, failing to
acquire this lock will abort QEMU when disk IO occurs.

We used to acquire aio_context as part of the bitmap lookup, so re-introduce
the lock for just the cases that have an IO penalty.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1672010
Reported-By: Aihua Liang <aliang@redhat.com>
---
 blockdev.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index fb18e9c975..790b0e0ac8 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2820,6 +2820,7 @@ void qmp_block_dirty_bitmap_add(const char *node, const char *name,
 {
     BlockDriverState *bs;
     BdrvDirtyBitmap *bitmap;
+    AioContext *aio_context = NULL;
 
     if (!name || name[0] == '\0') {
         error_setg(errp, "Bitmap name cannot be empty");
@@ -2854,15 +2855,17 @@ void qmp_block_dirty_bitmap_add(const char *node, const char *name,
         disabled = false;
     }
 
-    if (persistent &&
-        !bdrv_can_store_new_dirty_bitmap(bs, name, granularity, errp))
-    {
-        return;
+    if (persistent) {
+        aio_context = bdrv_get_aio_context(bs);
+        aio_context_acquire(aio_context);
+        if (!bdrv_can_store_new_dirty_bitmap(bs, name, granularity, errp)) {
+            goto out;
+        }
     }
 
     bitmap = bdrv_create_dirty_bitmap(bs, granularity, name, errp);
     if (bitmap == NULL) {
-        return;
+        goto out
     }
 
     if (disabled) {
@@ -2870,6 +2873,10 @@ void qmp_block_dirty_bitmap_add(const char *node, const char *name,
     }
 
     bdrv_dirty_bitmap_set_persistance(bitmap, persistent);
+ out:
+    if (aio_context) {
+        aio_context_release(aio_context);
+    }
 }
 
 void qmp_block_dirty_bitmap_remove(const char *node, const char *name,
@@ -2878,6 +2885,7 @@ void qmp_block_dirty_bitmap_remove(const char *node, const char *name,
     BlockDriverState *bs;
     BdrvDirtyBitmap *bitmap;
     Error *local_err = NULL;
+    AioContext *aio_context = NULL;
 
     bitmap = block_dirty_bitmap_lookup(node, name, &bs, errp);
     if (!bitmap || !bs) {
@@ -2892,14 +2900,20 @@ void qmp_block_dirty_bitmap_remove(const char *node, const char *name,
     }
 
     if (bdrv_dirty_bitmap_get_persistance(bitmap)) {
+        aio_context = bdrv_get_aio_context(bs);
+        aio_context_acquire(aio_context);
         bdrv_remove_persistent_dirty_bitmap(bs, name, &local_err);
         if (local_err != NULL) {
             error_propagate(errp, local_err);
-            return;
+            goto out;
         }
     }
 
     bdrv_release_dirty_bitmap(bs, bitmap);
+ out:
+    if (aio_context) {
+        aio_context_release(aio_context);
+    }
 }
 
 /**
-- 
2.17.2

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