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[PULL,3/4] block/io: Update BSC only if want_zero is true

Message ID 20220128230003.1114719-4-eblake@redhat.com
State New
Headers show
Series [PULL,1/4] nbd/server.c: Remove unused field | expand

Commit Message

Eric Blake Jan. 28, 2022, 11 p.m. UTC 
From: Hanna Reitz <hreitz@redhat.com>

We update the block-status cache whenever we get new information from a
bdrv_co_block_status() call to the block driver.  However, if we have
passed want_zero=false to that call, it may flag areas containing zeroes
as data, and so we would update the block-status cache with wrong
information.

Therefore, we should not update the cache with want_zero=false.

Reported-by: Nir Soffer <nsoffer@redhat.com>
Fixes: 0bc329fbb00 ("block: block-status cache for data regions")
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220118170000.49423-2-hreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/io.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
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Patch

diff --git a/block/io.c b/block/io.c
index bb0a254def11..4e4cb556c586 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2497,8 +2497,12 @@  static int coroutine_fn bdrv_co_block_status(BlockDriverState *bs,
              * non-protocol nodes, and then it is never used.  However, filling
              * the cache requires an RCU update, so double check here to avoid
              * such an update if possible.
+             *
+             * Check want_zero, because we only want to update the cache when we
+             * have accurate information about what is zero and what is data.
              */
-            if (ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
+            if (want_zero &&
+                ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
                 QLIST_EMPTY(&bs->children))
             {
                 /*