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commit: Drain nodes across all of bdrv_commit()

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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>
This commit is contained in:
Kevin Wolf
2026-04-27 19:05:17 +02:00
parent f27aea1896
commit f0d9ccd46c
1 changed files with 8 additions and 2 deletions
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10
block/commit.c
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@@ -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;
}