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From 4c6eff78f4b31ec4bd7b42440396760d19fde63e Mon Sep 17 00:00:00 2001
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From: Hanna Reitz <hreitz@redhat.com>
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Date: Tue, 18 Jan 2022 17:59:59 +0100
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Subject: [PATCH 6/7] block/io: Update BSC only if want_zero is true
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RH-Author: Hanna Reitz <hreitz@redhat.com>
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RH-MergeRequest: 112: block/io: Update BSC only if want_zero is true
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RH-Commit: [1/2] a202de1f52110d1e871c3b5b58f2d9e9b5d17570
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RH-Bugzilla: 2041480
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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We update the block-status cache whenever we get new information from a
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bdrv_co_block_status() call to the block driver. However, if we have
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passed want_zero=false to that call, it may flag areas containing zeroes
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as data, and so we would update the block-status cache with wrong
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information.
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Therefore, we should not update the cache with want_zero=false.
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Reported-by: Nir Soffer <nsoffer@redhat.com>
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Fixes: 0bc329fbb00 ("block: block-status cache for data regions")
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Reviewed-by: Nir Soffer <nsoffer@redhat.com>
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Cc: qemu-stable@nongnu.org
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Signed-off-by: Hanna Reitz <hreitz@redhat.com>
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Message-Id: <20220118170000.49423-2-hreitz@redhat.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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Signed-off-by: Eric Blake <eblake@redhat.com>
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(cherry picked from commit 113b727ce788335cf76f65355d670c9bc130fd75)
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Signed-off-by: Hanna Reitz <hreitz@redhat.com>
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---
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block/io.c | 6 +++++-
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1 file changed, 5 insertions(+), 1 deletion(-)
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diff --git a/block/io.c b/block/io.c
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index bb0a254def..4e4cb556c5 100644
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--- a/block/io.c
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+++ b/block/io.c
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@@ -2497,8 +2497,12 @@ static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs,
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* non-protocol nodes, and then it is never used. However, filling
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* the cache requires an RCU update, so double check here to avoid
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* such an update if possible.
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+ *
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+ * Check want_zero, because we only want to update the cache when we
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+ * have accurate information about what is zero and what is data.
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*/
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- if (ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
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+ if (want_zero &&
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+ ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
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QLIST_EMPTY(&bs->children))
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{
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/*
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--
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2.27.0
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