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From: | Vladimir Sementsov-Ogievskiy |
Subject: | Re: [PATCH 1/7] stream: Traverse graph after modification |
Date: | Wed, 10 Nov 2021 15:17:47 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 |
04.11.2021 13:38, Hanna Reitz wrote:
bdrv_cor_filter_drop() modifies the block graph. That means that other parties can also modify the block graph before it returns. Therefore, we cannot assume that the result of a graph traversal we did before remains valid afterwards. We should thus fetch `base` and `unfiltered_base` afterwards instead of before. Signed-off-by: Hanna Reitz <hreitz@redhat.com>
The fact that other parties can modify graph during our graph modification is a global problem.. The patch doesn't fix it, but reduces its effect in specific case.. OK. Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
--- block/stream.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/block/stream.c b/block/stream.c index 97bee482dc..e45113aed6 100644 --- a/block/stream.c +++ b/block/stream.c @@ -54,8 +54,8 @@ static int stream_prepare(Job *job) { StreamBlockJob *s = container_of(job, StreamBlockJob, common.job); BlockDriverState *unfiltered_bs = bdrv_skip_filters(s->target_bs); - BlockDriverState *base = bdrv_filter_or_cow_bs(s->above_base); - BlockDriverState *unfiltered_base = bdrv_skip_filters(base); + BlockDriverState *base; + BlockDriverState *unfiltered_base; Error *local_err = NULL; int ret = 0;@@ -63,6 +63,9 @@ static int stream_prepare(Job *job)bdrv_cor_filter_drop(s->cor_filter_bs); s->cor_filter_bs = NULL;+ base = bdrv_filter_or_cow_bs(s->above_base);+ unfiltered_base = bdrv_skip_filters(base); + if (bdrv_cow_child(unfiltered_bs)) { const char *base_id = NULL, *base_fmt = NULL; if (unfiltered_base) {
-- Best regards, Vladimir
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