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qcow2: Flush pending discards before allocating cluster

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Before a freed cluster can be reused, pending discards for this cluster
must be processed.

The original assumption was that this was not a problem because discards
are only cached during discard/write zeroes operations, which are
synchronous so that no concurrent write requests can cause cluster
allocations.

However, the discard/write zeroes operation itself can allocate a new L2
table (and it has to in order to put zero flags there), so make sure we
can cope with the situation.

This fixes https://bugs.launchpad.net/bugs/1349972.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Kevin Wolf 2015-05-06 13:21:51 +02:00
parent 8b6db32a4e
commit ecbda7a225
1 changed files with 5 additions and 0 deletions
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5
block/qcow2-refcount.c
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@ -833,6 +833,11 @@ static int64_t alloc_clusters_noref(BlockDriverState *bs, uint64_t size)
uint64_t i, nb_clusters, refcount;
int ret;
/* We can't allocate clusters if they may still be queued for discard. */
if (s->cache_discards) {
qcow2_process_discards(bs, 0);
}
nb_clusters = size_to_clusters(s, size);
retry:
for(i = 0; i < nb_clusters; i++) {