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[Qemu-devel] [PATCH] memory: Fix double unref of flatview

From: Matthew Rosato
Subject: [Qemu-devel] [PATCH] memory: Fix double unref of flatview
Date: Thu, 12 Feb 2015 11:21:31 -0500

Since 374f2981d1 "memory: protect current_map by RCU",
address_space_update_topology unrefs the old_flatview twice,
once by call_rcu and once by direct call.  This patch removes
the direct call in favor of the call_rcu.  Fixes at least one
assertion failure seen in s390, where a ref count for a memory
region attempts to go negative during hot-unplug of guest memory.

Signed-off-by: Matthew Rosato <address@hidden>
 memory.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/memory.c b/memory.c
index 130152c..d08abe5 100644
--- a/memory.c
+++ b/memory.c
@@ -755,7 +755,6 @@ static void address_space_update_topology(AddressSpace *as)
     /* Writes are protected by the BQL.  */
     atomic_rcu_set(&as->current_map, new_view);
-    call_rcu(old_view, flatview_unref, rcu);
     /* Note that all the old MemoryRegions are still alive up to this
      * point.  This relieves most MemoryListeners from the need to
@@ -763,7 +762,7 @@ static void address_space_update_topology(AddressSpace *as)
      * outside the iothread mutex, in which case precise reference
      * counting is necessary.
-    flatview_unref(old_view);
+    call_rcu(old_view, flatview_unref, rcu);

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