qemu-kvm/kvm-commit-Drain-nodes-across-all-of-bdrv_commit.patch

From 43fe4a491f9843019d780bfc41db44e86602f184 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Mon, 27 Apr 2026 19:05:17 +0200
Subject: [PATCH 47/52] commit: Drain nodes across all of bdrv_commit()

RH-Author: Kevin Wolf <kwolf@redhat.com>
RH-MergeRequest: 504: virt-storage: Backport stable branch fixes
RH-Jira: RHEL-186384
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Commit: [40/45] 29cfac9b1a72bf5d4b4497eb4096bc05d41e146e (kmwolf/centos-qemu-kvm)

The whole implementation of bdrv_commit() is only correct if no new
writes come in while it's running: It has only a single loop checking
the allocation status for each block and finally calls bdrv_make_empty()
without checking if that throws away any new changes.

We already have to drain while taking the graph write lock. Just extend
the drained section to all of bdrv_commit() to make sure that we don't
get any inconsistencies.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20260427170520.101242-2-kwolf@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Tested-by: Denis V. Lunev <den@openvz.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
(cherry picked from commit f0d9ccd46cf8fc576ab7d514f10f766546cdbc14)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/commit.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/block/commit.c b/block/commit.c
index 0d9e1a16d7..c5e3ef03a2 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -518,6 +518,7 @@ int bdrv_commit(BlockDriverState *bs)
     if (!drv)
         return -ENOMEDIUM;
 
+    bdrv_drain_all_begin();
     bdrv_graph_rdlock_main_loop();
 
     backing_file_bs = bdrv_cow_bs(bs);
@@ -549,6 +550,10 @@ int bdrv_commit(BlockDriverState *bs)
                   BLK_PERM_ALL);
     backing = blk_new(ctx, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
 
+    /* We drained all nodes, but still make requests through BlockBackends */
+    blk_set_disable_request_queuing(src, true);
+    blk_set_disable_request_queuing(backing, true);
+
     ret = blk_insert_bs(src, bs, &local_err);
     if (ret < 0) {
         error_report_err(local_err);
@@ -565,7 +570,7 @@ int bdrv_commit(BlockDriverState *bs)
 
     bdrv_graph_rdunlock_main_loop();
 
-    bdrv_graph_wrlock_drained();
+    bdrv_graph_wrlock();
     bdrv_set_backing_hd(commit_top_bs, backing_file_bs, &error_abort);
     bdrv_set_backing_hd(bs, commit_top_bs, &error_abort);
     bdrv_graph_wrunlock();
@@ -647,7 +652,7 @@ ro_cleanup:
     blk_unref(backing);
 
     bdrv_graph_rdunlock_main_loop();
-    bdrv_graph_wrlock_drained();
+    bdrv_graph_wrlock();
     if (bdrv_cow_bs(bs) != backing_file_bs) {
         bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
     }
@@ -663,6 +668,7 @@ ro_cleanup:
 
 out:
     bdrv_graph_rdunlock_main_loop();
+    bdrv_drain_all_end();
 
     return ret;
 }
-- 
2.52.0