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[Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in

From: Peter Maydell
Subject: [Qemu-devel] [PATCH] exec.c: Use atomic_rcu_read() to access dispatch in memory_region_section_get_iotlb()
Date: Mon, 20 Jul 2015 12:27:16 +0100

When accessing the dispatch pointer in an AddressSpace within an RCU
critical section we should always use atomic_rcu_read(). Fix an
access within memory_region_section_get_iotlb() which was incorrectly
doing a direct pointer access.

Signed-off-by: Peter Maydell <address@hidden>
I discussed this on IRC with Paolo a while back, and IIRC he said
that although this is a bug it's not one that can currently have
any ill effects, though I forget why (probably because this code
path is TCG only and TCG is single-threaded right now).

 exec.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/exec.c b/exec.c
index 7d60e15..0a4a0c5 100644
--- a/exec.c
+++ b/exec.c
@@ -954,7 +954,10 @@ hwaddr memory_region_section_get_iotlb(CPUState *cpu,
             iotlb |= PHYS_SECTION_ROM;
     } else {
-        iotlb = section - section->address_space->dispatch->map.sections;
+        AddressSpaceDispatch *d;
+        d = atomic_rcu_read(&section->address_space->dispatch);
+        iotlb = section - d->map.sections;
         iotlb += xlat;

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