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[PULL,for-4.1,3/7] include/qemu/atomic.h: Add signal_barrier

Message ID 20190714111249.13859-4-richard.henderson@linaro.org
State New
Headers show
Series [PULL,for-4.1,1/7] tcg: Fix constant folding of INDEX_op_extract2_i32 | expand

Commit Message

Richard Henderson July 14, 2019, 11:12 a.m. UTC 
We have some potential race conditions vs our user-exec signal
handler that will be solved with this barrier.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/qemu/atomic.h | 11 +++++++++++
 1 file changed, 11 insertions(+)
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Patch

diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index a6ac188188..f9cd24c899 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -88,6 +88,13 @@ 
 #define smp_read_barrier_depends()   barrier()
 #endif
 
+/*
+ * A signal barrier forces all pending local memory ops to be observed before
+ * a SIGSEGV is delivered to the *same* thread.  In practice this is exactly
+ * the same as barrier(), but since we have the correct builtin, use it.
+ */
+#define signal_barrier()    __atomic_signal_fence(__ATOMIC_SEQ_CST)
+
 /* Sanity check that the size of an atomic operation isn't "overly large".
  * Despite the fact that e.g. i686 has 64-bit atomic operations, we do not
  * want to use them because we ought not need them, and this lets us do a
@@ -308,6 +315,10 @@ 
 #define smp_read_barrier_depends()   barrier()
 #endif
 
+#ifndef signal_barrier
+#define signal_barrier()    barrier()
+#endif
+
 /* These will only be atomic if the processor does the fetch or store
  * in a single issue memory operation
  */