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Re: [Qemu-devel] [PATCH] qcow2: Flush pending discards before allocating

From: Max Reitz
Subject: Re: [Qemu-devel] [PATCH] qcow2: Flush pending discards before allocating cluster
Date: Wed, 06 May 2015 15:31:35 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 06.05.2015 13:29, Kevin Wolf wrote:
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

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.

Signed-off-by: Kevin Wolf <address@hidden>
  block/qcow2-refcount.c | 5 +++++
  1 file changed, 5 insertions(+)

Reviewed-by: Max Reitz <address@hidden>

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