From 04c5a9797c3bdf379ffad1f159eccfcdca12475f Mon Sep 17 00:00:00 2001
From: John Snow <jsnow@redhat.com>
Date: Wed, 20 Mar 2019 23:55:08 +0100
Subject: [PATCH 046/163] blockdev: acquire aio_context for bitmap add/remove

RH-Author: John Snow <jsnow@redhat.com>
Message-id: <20190320235508.17673-2-jsnow@redhat.com>
Patchwork-id: 85031
O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 1/1] blockdev: acquire aio_context for bitmap add/remove
Bugzilla: 1672010
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>

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. Commit 2119882c removed
these locks, and I failed to notice this when we committed fd5ae4cc, so this
has been broken since persistent bitmaps were introduced.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1672010
Reported-By: Aihua Liang <aliang@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20190218233154.19303-1-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>
(cherry picked from commit 0a6c86d024c52b1e66d4f7ec01a3bb8ea2600145)
Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 blockdev.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 47db9bb..f437896 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2973,6 +2973,7 @@ 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");
@@ -3007,15 +3008,17 @@ 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) {
@@ -3023,6 +3026,10 @@ 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,
@@ -3031,6 +3038,7 @@ 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) {
@@ -3045,14 +3053,20 @@ 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);
+    }
 }
 
 /**
-- 
1.8.3.1