[Qemu-devel] [RFC 6/8] cpu: atomically modify cpu->exit_request

["Alex Bennée" <alex.bennee@linaro.org>]

ThreadSanitizer picks up potential races although we already use
barriers to ensure things are in the correct order when processing exit
requests. For now we just use the relaxed atomic_set/atomic_read semantics
to reassure tsan that we can't tear the value.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 cpu-exec.c | 8 ++++----
 qom/cpu.c  | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index 9f4bd0b..113d8dc 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -192,7 +192,7 @@ static inline tcg_target_ulong cpu_tb_exec(CPUState *cpu, TranslationBlock *itb)
         /* We were asked to stop executing TBs (probably a pending
          * interrupt. We've now stopped, so clear the flag.
          */
-        cpu->tcg_exit_req = 0;
+        atomic_set(&cpu->tcg_exit_req, 0);
     }
     return ret;
 }
@@ -497,8 +497,8 @@ static inline void cpu_handle_interrupt(CPUState *cpu,
             *last_tb = NULL;
         }
     }
-    if (unlikely(cpu->exit_request || replay_has_interrupt())) {
-        cpu->exit_request = 0;
+    if (unlikely(atomic_read(&cpu->exit_request) || replay_has_interrupt())) {
+        atomic_set(&cpu->exit_request, 0);
         cpu->exception_index = EXCP_INTERRUPT;
         cpu_loop_exit(cpu);
     }
@@ -510,7 +510,7 @@ static inline void cpu_loop_exec_tb(CPUState *cpu, TranslationBlock *tb,
 {
     uintptr_t ret;
 
-    if (unlikely(cpu->exit_request)) {
+    if (unlikely(atomic_read(&cpu->exit_request))) {
         return;
     }
 
diff --git a/qom/cpu.c b/qom/cpu.c
index 2553247..47b1597 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -119,10 +119,10 @@ void cpu_reset_interrupt(CPUState *cpu, int mask)
 
 void cpu_exit(CPUState *cpu)
 {
-    cpu->exit_request = 1;
+    atomic_set(&cpu->exit_request, 1);
     /* Ensure cpu_exec will see the exit request after TCG has exited.  */
     smp_wmb();
-    cpu->tcg_exit_req = 1;
+    atomic_set(&cpu->tcg_exit_req, 1);
 }
 
 int cpu_write_elf32_qemunote(WriteCoreDumpFunction f, CPUState *cpu,
-- 
2.9.3