commit: Drain nodes across all of bdrv_commit()
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>
Kevin Wolf committed
Apr 27, 2026 at 19:05 UTC
f0d9ccd46cf8fc576ab7d514f10f766546cdbc14
1 file changed
+8
-2
block/commit.c
+8
-2
@@ -518,6 +518,7 @@ int bdrv_commit(BlockDriverState *bs)
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if (!drv)
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return -ENOMEDIUM;
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+ bdrv_drain_all_begin();
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bdrv_graph_rdlock_main_loop();
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backing_file_bs = bdrv_cow_bs(bs);
@@ -549,6 +550,10 @@ int bdrv_commit(BlockDriverState *bs)
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BLK_PERM_ALL);
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backing = blk_new(ctx, BLK_PERM_WRITE | BLK_PERM_RESIZE, BLK_PERM_ALL);
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+ /* We drained all nodes, but still make requests through BlockBackends */
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+ blk_set_disable_request_queuing(src, true);
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+ blk_set_disable_request_queuing(backing, true);
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+
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ret = blk_insert_bs(src, bs, &local_err);
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if (ret < 0) {
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error_report_err(local_err);
@@ -565,7 +570,7 @@ int bdrv_commit(BlockDriverState *bs)
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bdrv_graph_rdunlock_main_loop();
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- bdrv_graph_wrlock_drained();
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+ bdrv_graph_wrlock();
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bdrv_set_backing_hd(commit_top_bs, backing_file_bs, &error_abort);
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bdrv_set_backing_hd(bs, commit_top_bs, &error_abort);
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bdrv_graph_wrunlock();
@@ -647,7 +652,7 @@ ro_cleanup:
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blk_unref(backing);
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bdrv_graph_rdunlock_main_loop();
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- bdrv_graph_wrlock_drained();
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+ bdrv_graph_wrlock();
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if (bdrv_cow_bs(bs) != backing_file_bs) {
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bdrv_set_backing_hd(bs, backing_file_bs, &error_abort);
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}
@@ -663,6 +668,7 @@ ro_cleanup:
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out:
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bdrv_graph_rdunlock_main_loop();
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+ bdrv_drain_all_end();
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return ret;
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}